rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

JANUS INVESTMENT FUND

Prospectus Date

rr_ProspectusDate

Oct. 28, 2011

jif_SupplementTextBlock

Janus Investment Fund

Perkins Large Cap Value Fund

Supplement dated May 31, 2012

to Currently Effective Prospectuses

Effective May 31, 2012, the following replaces corresponding information for Perkins Large Cap Value Fund (the “Fund”).

1. The following replaces in its entirety the corresponding information found under “ANNUAL FUND OPERATING EXPENSES” in the Fund Summary section of the Fund’s Prospectus:


ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)	Class A		Class C		Class S		Class I		Class T

Management Fees (may adjust up or down)	0.67	%	0.67	%	0.67	%	0.67	%	0.67	%
Distribution/Service (12b-1) Fees	0.25	%	1.00	%	0.25	%	None		None
Other Expenses	0.22	%	0.30	%	0.39	%	0.17	%	0.39	%
Total Annual Fund Operating Expenses⁽¹⁾	1.14	%	1.97	%	1.31	%	0.84	%	1.06	%

(1)

Janus Capital has contractually agreed to waive the Fund’s total annual fund operating expenses (excluding any performance adjustments to management fees; the distribution and shareholder servicing fees – applicable to Class A Shares, Class C Shares, and Class S Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 1.00% until at least November 1, 2012. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

2. The following replaces in their entirety the corresponding example tables found under “EXAMPLE” in the Fund Summary section of the Fund’s Prospectus:


If Shares are redeemed:	1 Year		3 Years		5 Years		10 Years
Class A Shares	$	685	$	916	$	1,167	$	1,881
Class C Shares	$	300	$	618	$	1,062	$	2,296
Class S Shares	$	133	$	415	$	718	$	1,579
Class I Shares	$	86	$	268	$	466	$	1,037
Class T Shares	$	108	$	337	$	585	$	1,294


If Shares are not redeemed:	1 Year		3 Years		5 Years		10 Years
Class A Shares	$	685	$	916	$	1,167	$	1,881
Class C Shares	$	200	$	618	$	1,062	$	2,296
Class S Shares	$	133	$	415	$	718	$	1,579
Class I Shares	$	86	$	268	$	466	$	1,037
Class T Shares	$	108	$	337	$	585	$	1,294

3. The following replaces in its entirety the corresponding information found under “PERFORMANCE INFORMATION” in the Fund Summary section of the Fund’s Prospectus:

The following information provides some indication of the risks of investing in the Fund by showing how the Fund's performance has varied over time. Class I Shares, Class A Shares, Class C Shares, and Class S Shares of the Fund commenced operations on July 6, 2009, after the reorganization of each corresponding class of shares of Janus Adviser Perkins Large Cap Value Fund (“JAD predecessor fund”) into each respective share class of the Fund. Class T Shares of the Fund commenced operations on July 6, 2009.

•

The performance shown for Class I Shares, Class A Shares, Class C Shares, and Class S Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund's Class I Shares, Class A Shares, Class C Shares, and Class S Shares prior to the reorganization, calculated using the fees and expenses of each respective share class of the JAD predecessor fund, net of any applicable fee and expense limitations or waivers.


•	The performance shown for Class T Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund's Class I Shares prior to the reorganization, calculated using the fees and expenses of Class T Shares, without the effect of any fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.



Annual Total Returns for Class I Shares (calendar year-end)

	2009	2010	2011
	25.15%	12.19%	−0.20%

Best Quarter: Second Quarter 2009 15.40% Worst Quarter: Third Quarter 2011 −14.75%

The Fund’s year-to-date return as of the calendar quarter ended March 31, 2012 was 9.94%.


Average Annual Total Returns (periods ended 12/31/11)
	1 Year	Since Inception of Predecessor Fund (12/31/08)
Class I Shares

Return Before Taxes	−0.20%	11.90%

Return After Taxes on Distributions	−1.48%	11.09%

Return After Taxes on Distributions and Sale of Fund Shares⁽¹⁾	0.81%	10.04%

Russell 1000^® Value Index	0.39%	11.55%
(reflects no deduction for expenses, fees, or taxes)

Class A Shares

Return Before Taxes⁽²⁾	−6.25%	9.40%

Russell 1000^® Value Index	0.39%	11.55%
(reflects no deduction for expenses, fees, or taxes)

Class C Shares

Return Before Taxes⁽³⁾	−2.20%	10.74%

Russell 1000^® Value Index	0.39%	11.55%
(reflects no deduction for expenses, fees, or taxes)


Average Annual Total Returns (periods ended 12/31/11)
	1 Year	Since Inception of Predecessor Fund (12/31/08)

Class S Shares

Return Before Taxes	−0.72%	11.36%

Russell 1000^® Value Index	0.39%	11.55%
(reflects no deduction for expenses, fees, or taxes)

Class T Shares

Return Before Taxes	−0.41%	11.49%

Russell 1000^® Value Index	0.39%	11.55%
(reflects no deduction for expenses, fees, or taxes)


(1)	If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.
(2)	Calculated assuming maximum permitted sales loads.
(3)	The one year return is calculated to include the contingent deferred sales charge.

After-tax returns are calculated using distributions for the Fund’s Class I Shares for periods following July 6, 2009; and for the JAD predecessor fund’s Class I Shares for periods prior to July 6, 2009. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class I Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class I Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Please retain this Supplement with your records.

Janus Investment Fund

Perkins Large Cap Value Fund

Class D Shares

Supplement dated May 31, 2012

to Currently Effective Prospectuses

Effective May 31, 2012, the following replaces corresponding information for Perkins Large Cap Value Fund (the “Fund”).

1. The following replaces in its entirety the corresponding information found under “ANNUAL FUND OPERATING EXPENSES” in the Fund Summary section of the Fund’s Prospectus:



ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)							Class D

Management Fees (may adjust up or down)							0.67%
Other Expenses							0.29%
Total Annual Fund Operating Expenses⁽¹⁾							0.96%

(1)

Janus Capital has contractually agreed to waive the Fund’s total annual fund operating expenses (excluding any performance adjustments to management fees, administrative services fees payable pursuant to the Transfer Agency Agreement, brokerage commissions, interest, dividends, taxes, acquired fund fees and expenses, and extraordinary expenses) to 1.00% until at least November 1, 2012. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

2. The following replaces in its entirety the corresponding example table found under “EXAMPLE” in the Fund Summary section of the Fund’s Prospectus:


	1 Year		3 Years		5 Years		10 Years
Class D Shares	$	98	$	306	$	531	$	1,178

3. The following replaces in its entirety the corresponding information found under “PERFORMANCE INFORMATION” in the Fund Summary section of the Fund’s Prospectus:

The bar chart depicts the change in performance from year to year during the periods indicated. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.



Annual Total Returns for Class D Shares (calendar year-end)

	2009	2010	2011
	23.61%	11.94%	−0.37%

Best Quarter: Second Quarter 2009 15.02% Worst Quarter: Third Quarter 2011 −14.77%

The Fund’s year-to-date return as of the calendar quarter ended March 31, 2012 was 9.87%.


Average Annual Total Returns (periods ended 12/31/11)
	1 Year	Since Inception of Predecessor Fund (12/31/08)
Class D Shares

Return Before Taxes	−0.37%	11.29%

Return After Taxes on Distributions	−1.63%	10.50%

Return After Taxes on Distributions and Sale of Fund Shares⁽¹⁾	0.69%	9.52%

Russell 1000^® Value Index	0.39%	11.55%
(reflects no deduction for expenses, fees, or taxes)


(1)	If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

After-tax returns are calculated using distributions for the Fund’s Class D Shares for the periods following February 16, 2010; for the Fund’s Class I Shares for the period following July 6, 2009; and for the JAD predecessor fund’s Class I Shares for the period prior to July 6, 2009. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Please retain this Supplement with your records.

Janus Investment Fund

Perkins Small Cap Value Fund

Supplement dated May 31, 2012

to Currently Effective Prospectuses

Effective May 31, 2012, the following replaces corresponding information for Perkins Small Cap Value Fund (the “Fund”).

1. The following replaces in its entirety the corresponding information found under “ANNUAL FUND OPERATING EXPENSES” in the Fund Summary section of the Fund’s Prospectus:



ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)	Class A	Class C	Class S	Class I	Class R	Class T

Management Fees (may adjust up or down)	0.83%	0.83%	0.83%	0.83%	0.83%	0.83%
Distribution/Service (12b-1) Fees	0.25%	1.00%	0.25%	None	0.50%	None
Other Expenses	0.26%	0.30%	0.30%	0.15%	0.30%	0.30%
Total Annual Fund Operating Expenses⁽¹⁾	1.34%	2.13%	1.38%	0.98%	1.63%	1.13%
Fee Waiver⁽¹⁾	0.02%	0.06%	0.00%	0.00%	0.00%	0.00%
Net Annual Fund Operating Expenses After Fee Waiver⁽¹⁾	1.32%	2.07%	1.38%	0.98%	1.63%	1.13%

(1)

Janus Capital has contractually agreed to waive the Fund’s total annual fund operating expenses (excluding any performance adjustments to management fees; the distribution and shareholder servicing fees – applicable to Class A Shares, Class C Shares, Class S Shares, and Class R Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 0.96% until at least November 1, 2012. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

2. The following replaces in their entirety the corresponding example tables found under “EXAMPLE” in the Fund Summary section of the Fund’s Prospectus:


If Shares are redeemed:	1 Year		3 Years		5 Years		10 Years
Class A Shares	$	704	$	975	$	1,267	$	2,095
Class C Shares	$	316	$	667	$	1,144	$	2,462
Class S Shares	$	140	$	437	$	755	$	1,657
Class I Shares	$	100	$	312	$	542	$	1,201
Class R Shares	$	166	$	514	$	887	$	1,933
Class T Shares	$	115	$	359	$	622	$	1,375


If Shares are not redeemed:	1 Year		3 Years		5 Years		10 Years
Class A Shares	$	704	$	975	$	1,267	$	2,095
Class C Shares	$	216	$	667	$	1,144	$	2,462
Class S Shares	$	140	$	437	$	755	$	1,657
Class I Shares	$	100	$	312	$	542	$	1,201
Class R Shares	$	166	$	514	$	887	$	1,933
Class T Shares	$	115	$	359	$	622	$	1,375

3. The following replaces in its entirety the corresponding information found under “PERFORMANCE INFORMATION” in the Fund Summary section of the Fund’s Prospectus:

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class T Shares (formerly named Class J Shares) of the Fund commenced operations with the Fund’s inception. Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class R Shares of the Fund commenced operations on July 6, 2009.

•

The performance shown for Class T Shares for periods following April 21, 2003, reflects the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers. For the periods prior to April 21, 2003, the performance shown for Class T Shares reflects the historical performance of Berger Small Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Small Cap Value Fund – Investor Shares into the Fund’s former Class J Shares).


•	The performance shown for Class A Shares, Class C Shares, Class S Shares, and Class R Shares reflects the performance of the Fund’s Class J Shares (formerly named Investor Shares) from April 21, 2003 to July 6, 2009, calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers. For periods prior to April 21, 2003, the performance shown for Class A Shares, Class C Shares, Class S Shares, and Class R Shares reflects the historical performance of Berger Small Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Small Cap Value Fund – Investor Shares into the Fund’s former Class J Shares), calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers.
•	The performance shown for Class I Shares reflects the performance of the Fund’s Class J Shares (formerly named Investor Shares) from April 21, 2003 to July 6, 2009, calculated using the fees and expenses of Class J Shares, without the effect of any fee and expense limitations or waivers. For the periods prior to April 21, 2003, the performance shown for Class I Shares reflects the historical performance of Berger Small Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Small Cap Value Fund – Investor Shares into the Fund’s former Class J Shares), calculated using the fees and expenses of Class J Shares, without the effect of any fee and expense limitations or waivers.

If Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class R Shares of the Fund had been available during periods prior to July 6, 2009, the performance shown for each respective share class may have been different. The performance shown for periods following the Fund’s commencement of Class A Shares, Class C Shares, Class S Shares, Class I Shares, and Class R Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.



Annual Total Returns for Class T Shares (calendar year-end)

2002	2003	2004	2005	2006	2007	2008	2009	2010	2011
−15.59%	36.78%	13.57%	8.90%	12.37%	2.97%	−21.79%	36.59%	17.87%	−3.43%

Best Quarter: Second Quarter 2009 23.04% Worst Quarter: Third Quarter 2002 −22.57%

The Fund’s year-to-date return as of the calendar quarter ended March 31, 2012 was 8.15%.

Average Annual Total Returns (periods ended 12/31/11)

1 Year

5 Years

10 Years

Class T Shares

Return Before Taxes

−3.43%

4.60%

7.23%

Return After Taxes on Distributions

−5.87%

2.87%

5.36%

Return After Taxes on Distributions and Sale of Fund Shares⁽¹⁾

−0.57%

3.41%

5.73%

Russell 2000^® Value Index

−5.50%

−1.87%

6.40%

(reflects no deduction for expenses, fees, or taxes)

Class A Shares

Return Before Taxes⁽²⁾

−9.12%

3.17%

6.34%

Russell 2000^® Value Index

−5.50%

−1.87%

6.40%

(reflects no deduction for expenses, fees, or taxes)

Class C Shares

Return Before Taxes⁽³⁾

−5.21%

3.62%

6.22%

Russell 2000^® Value Index

−5.50%

−1.87%

6.40%

(reflects no deduction for expenses, fees, or taxes)

Class S Shares

Return Before Taxes

−3.69%

4.36%

6.98%

Russell 2000^® Value Index

−5.50%

−1.87%

6.40%

(reflects no deduction for expenses, fees, or taxes)

Class I Shares

Return Before Taxes

−3.28%

4.60%

7.23%

Russell 2000^® Value Index

−5.50%

−1.87%

6.40%

(reflects no deduction for expenses, fees, or taxes)

Class R Shares

Return Before Taxes

−3.89%

4.10%

6.72%

Russell 2000^® Value Index

−5.50%

−1.87%

6.40%

(reflects no deduction for expenses, fees, or taxes)


(1)	If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.
(2)	Calculated assuming maximum permitted sales loads.
(3)	The one year return is calculated to include the contingent deferred sales charge.

After-tax returns are calculated using distributions for the Fund’s Class T Shares (formerly named Class J Shares) for the periods following April 21, 2003; and for Berger Small Cap Value Fund – Investor Shares for periods prior to April 21, 2003. If Class T Shares of the Fund had been available during the periods prior to April 21, 2003, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class T Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class T Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

Please retain this Supplement with your records.

Janus Investment Fund

Perkins Small Cap Value Fund

Class D Shares

Supplement dated May 31, 2012

to Currently Effective Prospectuses

Effective May 31, 2012, the following replaces corresponding information for Perkins Small Cap Value Fund (the “Fund”).

1. The following replaces in its entirety the corresponding information found under “ANNUAL FUND OPERATING EXPENSES” in the Fund Summary section of the Fund’s Prospectus:



ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)							Class D

Management Fees (may adjust up or down)							0.83%
Other Expenses							0.20%
Total Annual Fund Operating Expenses⁽¹⁾							1.03%

(1)

Janus Capital has contractually agreed to waive the Fund’s total annual fund operating expenses (excluding any performance adjustments to management fees, administrative services fees payable pursuant to the Transfer Agency Agreement, brokerage commissions, interest, dividends, taxes, acquired fund fees and expenses, and extraordinary expenses) to 0.96% until at least November 1, 2012. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

2. The following replaces in its entirety the corresponding example table found under “EXAMPLE” in the Fund Summary section of the Fund’s Prospectus:


	1 Year		3 Years		5 Years		10 Years
Class D Shares	$	105	$	328	$	569	$	1,259

3. The following replaces in its entirety the corresponding information found under “PERFORMANCE INFORMATION” in the Fund Summary section of the Fund’s Prospectus:

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares (formerly named Investor Shares). For the periods prior to April 21, 2003, the performance shown for Class D Shares reflects the historical performance of Berger Small Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Small Cap Value Fund – Investor Shares into the Fund’s Class J Shares). If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.



Annual Total Returns for Class D Shares (calendar year-end)

2002	2003	2004	2005	2006	2007	2008	2009	2010	2011
−15.59%	36.78%	13.57%	8.90%	12.37%	2.97%	−21.79%	36.59%	18.00%	−3.33%

Best Quarter: Second Quarter 2009 23.04% Worst Quarter: Third Quarter 2002 −22.57%

The Fund’s year-to-date return as of the calendar quarter ended March 31, 2012 was 8.15%.

Average Annual Total Returns (periods ended 12/31/11)

1 Year

5 Years

10 Years

Class D Shares

Return Before Taxes

−3.33%

4.64%

7.25%

Return After Taxes on Distributions

−5.81%

2.91%

5.38%

Return After Taxes on Distributions and Sale of Fund Shares⁽¹⁾

−0.51%

3.44%

5.75%

Russell 2000^® Value Index

−5.50%

−1.87%

6.40%

(reflects no deduction for expenses, fees, or taxes)


(1)	If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

After-tax returns are calculated using distributions for the Fund’s Class D Shares for the periods following February 16, 2010; for the Fund’s Class J Shares (formerly named Investor Shares) for the period April 21, 2003 to February 16, 2010; and for Berger Small Cap Value Fund – Investor Shares for periods prior to April 21, 2003. If Class D Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Please retain this Supplement with your records.

Janus Investment Fund

Perkins Small Cap Value Fund

Class L Shares

Supplement dated May 31, 2012

to Currently Effective Prospectuses

Effective May 31, 2012, the following replaces corresponding information for Perkins Small Cap Value Fund (the “Fund”).

1. The following replaces in its entirety the corresponding information found under “ANNUAL FUND OPERATING EXPENSES” in the Fund Summary section of the Fund’s Prospectus:



ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)							Class L

Management Fees (may adjust up or down)							0.83%
Other Expenses							0.28%
Total Annual Fund Operating Expenses⁽¹⁾							1.11%

(1)

Janus Capital has contractually agreed to waive the Fund’s total annual fund operating expenses (excluding any performance adjustments to management fees, administrative services fees payable pursuant to the Transfer Agency Agreement, brokerage commissions, interest, dividends, taxes, acquired fund fees and expenses, and extraordinary expenses) to 0.96% until at least November 1, 2012. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

2. The following replaces in its entirety the corresponding example table found under “EXAMPLE” in the Fund Summary section of the Fund’s Prospectus:


	1 Year		3 Years		5 Years		10 Years
Class L Shares	$	113	$	353	$	612	$	1,352

3. The following replaces in its entirety the corresponding information found under “PERFORMANCE INFORMATION” in the Fund Summary section of the Fund’s Prospectus:



Annual Total Returns for Class L Shares (calendar year-end)

2002	2003	2004	2005	2006	2007	2008	2009	2010	2011
−15.33%	37.18%	13.80%	9.14%	12.57%	3.21%	−21.63%	36.91%	18.18%	−3.18%

Best Quarter: Second Quarter 2009 23.27% Worst Quarter: Third Quarter 2002 −22.47%

The Fund’s year-to-date return as of the calendar quarter ended March 31, 2012 was 8.21%.

Average Annual Total Returns (periods ended 12/31/11)

1 Year

5 Years

10 Years

Class L Shares

Return Before Taxes

−3.18%

4.85%

7.48%

Return After Taxes on Distributions

−5.68%

3.09%

5.58%

Return After Taxes on Distributions and Sale of Fund Shares⁽¹⁾

−0.43%

3.60%

5.93%

Russell 2000^® Value Index

−5.50%

−1.87%

6.40%

(reflects no deduction for expenses, fees, or taxes)


(1)	If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

After-tax returns are calculated using distributions for the Fund’s Class L Shares (formerly named Institutional Shares) for the periods following April 21, 2003; and for Berger Small Cap Value Fund – Institutional Shares for periods prior to April 21, 2003. If Class L Shares of the Fund had been available during these earlier periods, distributions may have been different and thus, after-tax returns may have been different from those shown. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

Please retain this Supplement with your records.

Perkins Large Cap Value Fund | Class A, C, S, I, T Shares

rr_RiskReturnAbstract

jif_SupplementTextBlock

Janus Investment Fund

Perkins Large Cap Value Fund

Supplement dated May 31, 2012

to Currently Effective Prospectuses

Effective May 31, 2012, the following replaces corresponding information for Perkins Large Cap Value Fund (the “Fund”).

1. The following replaces in its entirety the corresponding information found under “ANNUAL FUND OPERATING EXPENSES” in the Fund Summary section of the Fund’s Prospectus:


ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)	Class A		Class C		Class S		Class I		Class T

Management Fees (may adjust up or down)	0.67	%	0.67	%	0.67	%	0.67	%	0.67	%
Distribution/Service (12b-1) Fees	0.25	%	1.00	%	0.25	%	None		None
Other Expenses	0.22	%	0.30	%	0.39	%	0.17	%	0.39	%
Total Annual Fund Operating Expenses⁽¹⁾	1.14	%	1.97	%	1.31	%	0.84	%	1.06	%

(1)

2. The following replaces in their entirety the corresponding example tables found under “EXAMPLE” in the Fund Summary section of the Fund’s Prospectus:


If Shares are redeemed:	1 Year		3 Years		5 Years		10 Years
Class A Shares	$	685	$	916	$	1,167	$	1,881
Class C Shares	$	300	$	618	$	1,062	$	2,296
Class S Shares	$	133	$	415	$	718	$	1,579
Class I Shares	$	86	$	268	$	466	$	1,037
Class T Shares	$	108	$	337	$	585	$	1,294


If Shares are not redeemed:	1 Year		3 Years		5 Years		10 Years
Class A Shares	$	685	$	916	$	1,167	$	1,881
Class C Shares	$	200	$	618	$	1,062	$	2,296
Class S Shares	$	133	$	415	$	718	$	1,579
Class I Shares	$	86	$	268	$	466	$	1,037
Class T Shares	$	108	$	337	$	585	$	1,294

3. The following replaces in its entirety the corresponding information found under “PERFORMANCE INFORMATION” in the Fund Summary section of the Fund’s Prospectus:

•


•	The performance shown for Class T Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund's Class I Shares prior to the reorganization, calculated using the fees and expenses of Class T Shares, without the effect of any fee and expense limitations or waivers.



Annual Total Returns for Class I Shares (calendar year-end)

	2009	2010	2011
	25.15%	12.19%	−0.20%

Best Quarter: Second Quarter 2009 15.40% Worst Quarter: Third Quarter 2011 −14.75%

The Fund’s year-to-date return as of the calendar quarter ended March 31, 2012 was 9.94%.


Average Annual Total Returns (periods ended 12/31/11)
	1 Year	Since Inception of Predecessor Fund (12/31/08)
Class I Shares

Return Before Taxes	−0.20%	11.90%

Return After Taxes on Distributions	−1.48%	11.09%

Return After Taxes on Distributions and Sale of Fund Shares⁽¹⁾	0.81%	10.04%

Russell 1000^® Value Index	0.39%	11.55%
(reflects no deduction for expenses, fees, or taxes)

Class A Shares

Return Before Taxes⁽²⁾	−6.25%	9.40%

Russell 1000^® Value Index	0.39%	11.55%
(reflects no deduction for expenses, fees, or taxes)

Class C Shares

Return Before Taxes⁽³⁾	−2.20%	10.74%

Russell 1000^® Value Index	0.39%	11.55%
(reflects no deduction for expenses, fees, or taxes)


Average Annual Total Returns (periods ended 12/31/11)
	1 Year	Since Inception of Predecessor Fund (12/31/08)

Class S Shares

Return Before Taxes	−0.72%	11.36%

Russell 1000^® Value Index	0.39%	11.55%
(reflects no deduction for expenses, fees, or taxes)

Class T Shares

Return Before Taxes	−0.41%	11.49%

Russell 1000^® Value Index	0.39%	11.55%
(reflects no deduction for expenses, fees, or taxes)


(1)	If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.
(2)	Calculated assuming maximum permitted sales loads.
(3)	The one year return is calculated to include the contingent deferred sales charge.

Please retain this Supplement with your records.

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

November 1, 2012

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

If Shares are redeemed:

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

If Shares are not redeemed:

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund's performance has varied over time. Class I Shares, Class A Shares, Class C Shares, and Class S Shares of the Fund commenced operations on July 6, 2009, after the reorganization of each corresponding class of shares of Janus Adviser Perkins Large Cap Value Fund ("JAD predecessor fund") into each respective share class of the Fund. Class T Shares of the Fund commenced operations on July 6, 2009.

The performance shown for Class I Shares, Class A Shares, Class C Shares, and Class S Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund's Class I Shares, Class A Shares, Class C Shares, and Class S Shares prior to the reorganization, calculated using the fees and expenses of each respective share class of the JAD predecessor fund, net of any applicable fee and expense limitations or waivers.

The performance shown for Class T Shares for periods prior to July 6, 2009, reflects the historical performance of the JAD predecessor fund's Class I Shares prior to the reorganization, calculated using the fees and expenses of Class T Shares, without the effect of any fee and expense limitations or waivers.

If Class T Shares of the Fund had been available during periods prior to July 6, 2009, the performance shown may have been different. The performance shown for periods following the Fund's commencement of Class I Shares, Class A Shares, Class C Shares, Class S Shares, and Class T Shares reflects the fees and expenses of each respective share class, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower. The table compares the Fund's average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund's performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.
The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund's performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

rr_PerformanceAdditionalMarketIndex

The table compares the Fund's average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions.

rr_PerformanceAvailabilityPhone

1-877-335-2687

rr_PerformanceAvailabilityWebSiteAddress

janus.com/advisor/mutual-funds

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartHeading

Annual Total Returns for Class I Shares (calendar year-end)

rr_BarChartDoesNotReflectSalesLoads

The bar chart figures do not include any applicable sales charges that an investor may pay when they buy or sell Class A Shares or Class C Shares of the Fund. If sales charges were included, the returns would be lower.

rr_BarChartClosingTextBlock

Best Quarter: Second Quarter 2009 15.40% Worst Quarter: Third Quarter 2011 -14.75%

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

rr_PerformanceTableOneClassOfAfterTaxShown

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

rr_PerformanceTableNarrativeTextBlock

After-tax returns are calculated using distributions for the Fund's Class I Shares for periods following July 6, 2009; and for the JAD predecessor fund's Class I Shares for periods prior to July 6, 2009. After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on your individual tax situation and may differ from those shown in the preceding table. The after-tax return information shown above does not apply to Fund shares held through a tax-deferred account, such as a 401(k) plan or an IRA.

After-tax returns are only shown for Class I Shares of the Fund. After-tax returns for the other classes of Shares will vary from those shown for Class I Shares due to varying sales charges (as applicable), fees, and expenses among the classes.

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Perkins Large Cap Value Fund | Class A, C, S, I, T Shares | Class A

rr_RiskReturnAbstract

rr_OperatingExpensesColumnName

Class A

rr_ManagementFeesOverAssets

0.67%

rr_DistributionAndService12b1FeesOverAssets

0.25%

rr_OtherExpensesOverAssets

0.22%

rr_ExpensesOverAssets

1.14%

^[1]

rr_ExpenseExampleByYearColumnName

Class A Shares

rr_ExpenseExampleYear01

685

rr_ExpenseExampleYear03

916

rr_ExpenseExampleYear05

1,167

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleYear10

1,881

rr_ExpenseExampleNoRedemptionByYearColumnName

Class A Shares

rr_ExpenseExampleNoRedemptionYear01

685

rr_ExpenseExampleNoRedemptionYear03

916

rr_ExpenseExampleNoRedemptionYear05

1,167

rr_ExpenseExampleNoRedemptionYear10

1,881

Perkins Large Cap Value Fund | Class A, C, S, I, T Shares | Class C

rr_RiskReturnAbstract

rr_OperatingExpensesColumnName

Class C

rr_ManagementFeesOverAssets

0.67%

rr_DistributionAndService12b1FeesOverAssets

1.00%

rr_OtherExpensesOverAssets

0.30%

rr_ExpensesOverAssets

1.97%

^[1]

rr_ExpenseExampleByYearColumnName

Class C Shares

rr_ExpenseExampleYear01

300

rr_ExpenseExampleYear03

618

rr_ExpenseExampleYear05

1,062

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleYear10

2,296

rr_ExpenseExampleNoRedemptionByYearColumnName

Class C Shares

rr_ExpenseExampleNoRedemptionYear01

200

rr_ExpenseExampleNoRedemptionYear03

618

rr_ExpenseExampleNoRedemptionYear05

1,062

rr_ExpenseExampleNoRedemptionYear10

2,296

Perkins Large Cap Value Fund | Class A, C, S, I, T Shares | Class S

rr_RiskReturnAbstract

rr_OperatingExpensesColumnName

Class S

rr_ManagementFeesOverAssets

0.67%

rr_DistributionAndService12b1FeesOverAssets

0.25%

rr_OtherExpensesOverAssets

0.39%

rr_ExpensesOverAssets

1.31%

^[1]

rr_ExpenseExampleByYearColumnName

Class S Shares

rr_ExpenseExampleYear01

133

rr_ExpenseExampleYear03

415

rr_ExpenseExampleYear05

718

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleYear10

1,579

rr_ExpenseExampleNoRedemptionByYearColumnName

Class S Shares

rr_ExpenseExampleNoRedemptionYear01

133

rr_ExpenseExampleNoRedemptionYear03

415

rr_ExpenseExampleNoRedemptionYear05

718

rr_ExpenseExampleNoRedemptionYear10

1,579

Perkins Large Cap Value Fund | Class A, C, S, I, T Shares | Class I

rr_RiskReturnAbstract

rr_OperatingExpensesColumnName

Class I

rr_ManagementFeesOverAssets

0.67%

rr_DistributionAndService12b1FeesOverAssets

none

rr_OtherExpensesOverAssets

0.17%

rr_ExpensesOverAssets

0.84%

^[1]

rr_ExpenseExampleByYearColumnName

Class I Shares

rr_ExpenseExampleYear01

rr_ExpenseExampleYear03

268

rr_ExpenseExampleYear05

466

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleYear10

1,037

rr_ExpenseExampleNoRedemptionByYearColumnName

Class I Shares

rr_ExpenseExampleNoRedemptionYear01

rr_ExpenseExampleNoRedemptionYear03

268

rr_ExpenseExampleNoRedemptionYear05

466

rr_ExpenseExampleNoRedemptionYear10

1,037

rr_AnnualReturn2009

25.15%

rr_AnnualReturn2010

12.19%

rr_AnnualReturn2011

(0.20%)

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended March 31, 2012 was 9.94%.

rr_BarChartYearToDateReturnDate

Mar. 31, 2012

rr_BarChartYearToDateReturn

9.94%

rr_HighestQuarterlyReturnLabel

Best Quarter:

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

rr_BarChartHighestQuarterlyReturn

15.40%

rr_LowestQuarterlyReturnLabel

Worst Quarter:

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

rr_BarChartLowestQuarterlyReturn

(14.75%)

Perkins Large Cap Value Fund | Class A, C, S, I, T Shares | Class T

rr_RiskReturnAbstract

rr_OperatingExpensesColumnName

Class T

rr_ManagementFeesOverAssets

0.67%

rr_DistributionAndService12b1FeesOverAssets

none

rr_OtherExpensesOverAssets

0.39%

rr_ExpensesOverAssets

1.06%

^[1]

rr_ExpenseExampleByYearColumnName

Class T Shares

rr_ExpenseExampleYear01

108

rr_ExpenseExampleYear03

337

rr_ExpenseExampleYear05

585

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleYear10

1,294

rr_ExpenseExampleNoRedemptionByYearColumnName

Class T Shares

rr_ExpenseExampleNoRedemptionYear01

108

rr_ExpenseExampleNoRedemptionYear03

337

rr_ExpenseExampleNoRedemptionYear05

585

rr_ExpenseExampleNoRedemptionYear10

1,294

Perkins Large Cap Value Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class A

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class A Shares

rr_AverageAnnualReturnLabel

Return Before Taxes

^[2]

rr_AverageAnnualReturnYear01

(6.25%)

rr_AverageAnnualReturnSinceInception

9.40%

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

Perkins Large Cap Value Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class C

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class C Shares

rr_AverageAnnualReturnLabel

Return Before Taxes

^[3]

rr_AverageAnnualReturnYear01

(2.20%)

rr_AverageAnnualReturnSinceInception

10.74%

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

Perkins Large Cap Value Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class S

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class S Shares

rr_AverageAnnualReturnLabel

Return Before Taxes

rr_AverageAnnualReturnYear01

(0.72%)

rr_AverageAnnualReturnSinceInception

11.36%

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

Perkins Large Cap Value Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class I

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class I Shares

rr_AverageAnnualReturnLabel

Return Before Taxes

rr_AverageAnnualReturnYear01

(0.20%)

rr_AverageAnnualReturnSinceInception

11.90%

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

Perkins Large Cap Value Fund | Class A, C, S, I, T Shares | Return Before Taxes | Class T

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class T Shares

rr_AverageAnnualReturnLabel

Return Before Taxes

rr_AverageAnnualReturnYear01

(0.41%)

rr_AverageAnnualReturnSinceInception

11.49%

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

Perkins Large Cap Value Fund | Class A, C, S, I, T Shares | Return After Taxes on Distributions | Class I

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class I

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

rr_AverageAnnualReturnYear01

(1.48%)

rr_AverageAnnualReturnSinceInception

11.09%

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

Perkins Large Cap Value Fund | Class A, C, S, I, T Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class I

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class I

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[4]

rr_AverageAnnualReturnYear01

0.81%

rr_AverageAnnualReturnSinceInception

10.04%

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

Perkins Large Cap Value Fund | Class A, C, S, I, T Shares | Russell 1000 Value Index (reflects no deduction for expenses, fees, or taxes)

rr_RiskReturnAbstract

rr_AverageAnnualReturnLabel

Russell 1000^® Value Index

rr_AverageAnnualReturnYear01

0.39%

rr_AverageAnnualReturnSinceInception

11.55%

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

Perkins Large Cap Value Fund | Class D Shares

rr_RiskReturnAbstract

jif_SupplementTextBlock

Janus Investment Fund

Perkins Large Cap Value Fund

Class D Shares

Supplement dated May 31, 2012

to Currently Effective Prospectuses

Effective May 31, 2012, the following replaces corresponding information for Perkins Large Cap Value Fund (the “Fund”).

1. The following replaces in its entirety the corresponding information found under “ANNUAL FUND OPERATING EXPENSES” in the Fund Summary section of the Fund’s Prospectus:



ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)							Class D

Management Fees (may adjust up or down)							0.67%
Other Expenses							0.29%
Total Annual Fund Operating Expenses⁽¹⁾							0.96%

(1)

2. The following replaces in its entirety the corresponding example table found under “EXAMPLE” in the Fund Summary section of the Fund’s Prospectus:


	1 Year		3 Years		5 Years		10 Years
Class D Shares	$	98	$	306	$	531	$	1,178

3. The following replaces in its entirety the corresponding information found under “PERFORMANCE INFORMATION” in the Fund Summary section of the Fund’s Prospectus:



Annual Total Returns for Class D Shares (calendar year-end)

	2009	2010	2011
	23.61%	11.94%	−0.37%

Best Quarter: Second Quarter 2009 15.02% Worst Quarter: Third Quarter 2011 −14.77%

The Fund’s year-to-date return as of the calendar quarter ended March 31, 2012 was 9.87%.


Average Annual Total Returns (periods ended 12/31/11)
	1 Year	Since Inception of Predecessor Fund (12/31/08)
Class D Shares

Return Before Taxes	−0.37%	11.29%

Return After Taxes on Distributions	−1.63%	10.50%

Return After Taxes on Distributions and Sale of Fund Shares⁽¹⁾	0.69%	9.52%

Russell 1000^® Value Index	0.39%	11.55%
(reflects no deduction for expenses, fees, or taxes)


(1)	If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Please retain this Supplement with your records.

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

November 1, 2012

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010. The performance shown for Class D Shares for the period July 6, 2009 to February 16, 2010, reflects the performance of the Fund’s Class I Shares, calculated using the fees and expenses of Class D Shares, without the effect of any fee and expense limitations or waivers. Performance shown for the period prior to July 6, 2009, reflects the historical performance of the Janus Adviser Perkins Large Cap Value Fund’s (“JAD predecessor fund”) Class I Shares prior to the reorganization of Class I Shares of the JAD predecessor fund into Class I Shares of the Fund, calculated using the fees and expenses of Class D Shares, without the effect of any fee and expense limitations or waivers. If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.

The bar chart depicts the change in performance from year to year during the periods indicated. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.
The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

rr_PerformanceInformationIllustratesVariabilityOfReturns

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time.

The bar chart depicts the change in performance from year to year during the periods indicated.

rr_PerformanceAdditionalMarketIndex

rr_PerformanceAvailabilityPhone

1-800-525-3713

rr_PerformanceAvailabilityWebSiteAddress

janus.com/allfunds

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

rr_BarChartHeading

Annual Total Returns for Class D Shares (calendar year-end)

rr_BarChartClosingTextBlock

Best Quarter: Second Quarter 2009 15.02% Worst Quarter: Third Quarter 2011 -14.77%

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

rr_PerformanceTableNotRelevantToTaxDeferred

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund's other return figures.

rr_PerformanceTableNarrativeTextBlock

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Perkins Large Cap Value Fund | Class D Shares | Class D

rr_RiskReturnAbstract

rr_OperatingExpensesColumnName

Class D

rr_ManagementFeesOverAssets

0.67%

rr_OtherExpensesOverAssets

0.29%

rr_ExpensesOverAssets

0.96%

^[5]

rr_ExpenseExampleByYearColumnName

Class D Shares

rr_ExpenseExampleYear01

rr_ExpenseExampleYear03

306

rr_ExpenseExampleYear05

531

rr_ExpenseExampleYear10

1,178

rr_AnnualReturn2009

23.61%

rr_AnnualReturn2010

11.94%

rr_AnnualReturn2011

(0.37%)

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended March 31, 2012 was 9.87%.

rr_BarChartYearToDateReturnDate

Mar. 31, 2012

rr_BarChartYearToDateReturn

9.87%

rr_HighestQuarterlyReturnLabel

Best Quarter:

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

rr_BarChartHighestQuarterlyReturn

15.02%

rr_LowestQuarterlyReturnLabel

Worst Quarter:

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2011

rr_BarChartLowestQuarterlyReturn

(14.77%)

Perkins Large Cap Value Fund | Class D Shares | Return Before Taxes | Class D

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class D Shares

rr_AverageAnnualReturnLabel

Return Before Taxes

rr_AverageAnnualReturnYear01

(0.37%)

rr_AverageAnnualReturnSinceInception

11.29%

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

Perkins Large Cap Value Fund | Class D Shares | Return After Taxes on Distributions | Class D

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class D Shares

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

rr_AverageAnnualReturnYear01

(1.63%)

rr_AverageAnnualReturnSinceInception

10.50%

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

Perkins Large Cap Value Fund | Class D Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class D

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class D Shares

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[4]

rr_AverageAnnualReturnYear01

0.69%

rr_AverageAnnualReturnSinceInception

9.52%

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

Perkins Large Cap Value Fund | Class D Shares | Russell 1000 Value Index (reflects no deduction for expenses, fees, or taxes) | Class D

rr_RiskReturnAbstract

rr_AverageAnnualReturnLabel

Russell 1000^® Value Index

rr_AverageAnnualReturnYear01

0.39%

rr_AverageAnnualReturnSinceInception

11.55%

rr_AverageAnnualReturnInceptionDate

Dec. 31, 2008

Perkins Small Cap Value Fund | Class A, C, S, I, R, T Shares

rr_RiskReturnAbstract

jif_SupplementTextBlock

Janus Investment Fund

Perkins Small Cap Value Fund

Supplement dated May 31, 2012

to Currently Effective Prospectuses

Effective May 31, 2012, the following replaces corresponding information for Perkins Small Cap Value Fund (the “Fund”).

1. The following replaces in its entirety the corresponding information found under “ANNUAL FUND OPERATING EXPENSES” in the Fund Summary section of the Fund’s Prospectus:



ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)	Class A	Class C	Class S	Class I	Class R	Class T

Management Fees (may adjust up or down)	0.83%	0.83%	0.83%	0.83%	0.83%	0.83%
Distribution/Service (12b-1) Fees	0.25%	1.00%	0.25%	None	0.50%	None
Other Expenses	0.26%	0.30%	0.30%	0.15%	0.30%	0.30%
Total Annual Fund Operating Expenses⁽¹⁾	1.34%	2.13%	1.38%	0.98%	1.63%	1.13%
Fee Waiver⁽¹⁾	0.02%	0.06%	0.00%	0.00%	0.00%	0.00%
Net Annual Fund Operating Expenses After Fee Waiver⁽¹⁾	1.32%	2.07%	1.38%	0.98%	1.63%	1.13%

(1)

Janus Capital has contractually agreed to waive the Fund’s total annual fund operating expenses (excluding any performance adjustments to management fees; the distribution and shareholder servicing fees – applicable to Class A Shares, Class C Shares, Class S Shares, and Class R Shares; administrative services fees payable pursuant to the Transfer Agency Agreement (except for networking and omnibus fees); brokerage commissions; interest; dividends; taxes; acquired fund fees and expenses; and extraordinary expenses) to 0.96% until at least November 1, 2012. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

2. The following replaces in their entirety the corresponding example tables found under “EXAMPLE” in the Fund Summary section of the Fund’s Prospectus:


If Shares are redeemed:	1 Year		3 Years		5 Years		10 Years
Class A Shares	$	704	$	975	$	1,267	$	2,095
Class C Shares	$	316	$	667	$	1,144	$	2,462
Class S Shares	$	140	$	437	$	755	$	1,657
Class I Shares	$	100	$	312	$	542	$	1,201
Class R Shares	$	166	$	514	$	887	$	1,933
Class T Shares	$	115	$	359	$	622	$	1,375


If Shares are not redeemed:	1 Year		3 Years		5 Years		10 Years
Class A Shares	$	704	$	975	$	1,267	$	2,095
Class C Shares	$	216	$	667	$	1,144	$	2,462
Class S Shares	$	140	$	437	$	755	$	1,657
Class I Shares	$	100	$	312	$	542	$	1,201
Class R Shares	$	166	$	514	$	887	$	1,933
Class T Shares	$	115	$	359	$	622	$	1,375

3. The following replaces in its entirety the corresponding information found under “PERFORMANCE INFORMATION” in the Fund Summary section of the Fund’s Prospectus:

•


•	The performance shown for Class A Shares, Class C Shares, Class S Shares, and Class R Shares reflects the performance of the Fund’s Class J Shares (formerly named Investor Shares) from April 21, 2003 to July 6, 2009, calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers. For periods prior to April 21, 2003, the performance shown for Class A Shares, Class C Shares, Class S Shares, and Class R Shares reflects the historical performance of Berger Small Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Small Cap Value Fund – Investor Shares into the Fund’s former Class J Shares), calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers.
•	The performance shown for Class I Shares reflects the performance of the Fund’s Class J Shares (formerly named Investor Shares) from April 21, 2003 to July 6, 2009, calculated using the fees and expenses of Class J Shares, without the effect of any fee and expense limitations or waivers. For the periods prior to April 21, 2003, the performance shown for Class I Shares reflects the historical performance of Berger Small Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Small Cap Value Fund – Investor Shares into the Fund’s former Class J Shares), calculated using the fees and expenses of Class J Shares, without the effect of any fee and expense limitations or waivers.



Annual Total Returns for Class T Shares (calendar year-end)

2002	2003	2004	2005	2006	2007	2008	2009	2010	2011
−15.59%	36.78%	13.57%	8.90%	12.37%	2.97%	−21.79%	36.59%	17.87%	−3.43%

Best Quarter: Second Quarter 2009 23.04% Worst Quarter: Third Quarter 2002 −22.57%

The Fund’s year-to-date return as of the calendar quarter ended March 31, 2012 was 8.15%.

Average Annual Total Returns (periods ended 12/31/11)

1 Year

5 Years

10 Years

Class T Shares

Return Before Taxes

−3.43%

4.60%

7.23%

Return After Taxes on Distributions

−5.87%

2.87%

5.36%

Return After Taxes on Distributions and Sale of Fund Shares⁽¹⁾

−0.57%

3.41%

5.73%

Russell 2000^® Value Index

−5.50%

−1.87%

6.40%

(reflects no deduction for expenses, fees, or taxes)

Class A Shares

Return Before Taxes⁽²⁾

−9.12%

3.17%

6.34%

Russell 2000^® Value Index

−5.50%

−1.87%

6.40%

(reflects no deduction for expenses, fees, or taxes)

Class C Shares

Return Before Taxes⁽³⁾

−5.21%

3.62%

6.22%

Russell 2000^® Value Index

−5.50%

−1.87%

6.40%

(reflects no deduction for expenses, fees, or taxes)

Class S Shares

Return Before Taxes

−3.69%

4.36%

6.98%

Russell 2000^® Value Index

−5.50%

−1.87%

6.40%

(reflects no deduction for expenses, fees, or taxes)

Class I Shares

Return Before Taxes

−3.28%

4.60%

7.23%

Russell 2000^® Value Index

−5.50%

−1.87%

6.40%

(reflects no deduction for expenses, fees, or taxes)

Class R Shares

Return Before Taxes

−3.89%

4.10%

6.72%

Russell 2000^® Value Index

−5.50%

−1.87%

6.40%

(reflects no deduction for expenses, fees, or taxes)


(1)	If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.
(2)	Calculated assuming maximum permitted sales loads.
(3)	The one year return is calculated to include the contingent deferred sales charge.

Please retain this Supplement with your records.

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

November 1, 2012

Expense Example by, Year, Caption [Text]

rr_ExpenseExampleByYearCaption

If Shares are redeemed:

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

If Shares are not redeemed:

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceNarrativeTextBlock

The performance shown for Class T Shares for periods following April 21, 2003, reflects the fees and expenses of Class T Shares in effect during the periods shown, net of any applicable fee and expense limitations or waivers. For the periods prior to April 21, 2003, the performance shown for Class T Shares reflects the historical performance of Berger Small Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Small Cap Value Fund – Investor Shares into the Fund’s former Class J Shares).
The performance shown for Class A Shares, Class C Shares, Class S Shares, and Class R Shares reflects the performance of the Fund’s Class J Shares (formerly named Investor Shares) from April 21, 2003 to July 6, 2009, calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers. For periods prior to April 21, 2003, the performance shown for Class A Shares, Class C Shares, Class S Shares, and Class R Shares reflects the historical performance of Berger Small Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Small Cap Value Fund – Investor Shares into the Fund’s former Class J Shares), calculated using the fees and expenses of each respective share class, without the effect of any fee and expense limitations or waivers.
The performance shown for Class I Shares reflects the performance of the Fund’s Class J Shares (formerly named Investor Shares) from April 21, 2003 to July 6, 2009, calculated using the fees and expenses of Class J Shares, without the effect of any fee and expense limitations or waivers. For the periods prior to April 21, 2003, the performance shown for Class I Shares reflects the historical performance of Berger Small Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Small Cap Value Fund – Investor Shares into the Fund’s former Class J Shares), calculated using the fees and expenses of Class J Shares, without the effect of any fee and expense limitations or waivers.

rr_PerformanceInformationIllustratesVariabilityOfReturns

rr_PerformanceAdditionalMarketIndex

The table compares the Funḏs average annual returns for the periods indicated to broad-based securities market indices. The indices are not actively managed and are not available for direct investment. All figures assume reinvestment of dividends and distributions.

rr_PerformanceAvailabilityPhone

1-877-335-2687

rr_PerformanceAvailabilityWebSiteAddress

janus.com/advisor/mutual-funds

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartHeading

Annual Total Returns for Class T Shares (calendar year-end)

rr_BarChartDoesNotReflectSalesLoads

rr_BarChartClosingTextBlock

Best Quarter: Second Quarter 2009 23.04% Worst Quarter: Third Quarter 2002 -22.57%

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableNotRelevantToTaxDeferred

rr_PerformanceTableOneClassOfAfterTaxShown

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

rr_PerformanceTableNarrativeTextBlock

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Perkins Small Cap Value Fund | Class A, C, S, I, R, T Shares | Class A

rr_RiskReturnAbstract

rr_OperatingExpensesColumnName

Class A

rr_ManagementFeesOverAssets

0.83%

rr_DistributionAndService12b1FeesOverAssets

0.25%

rr_OtherExpensesOverAssets

0.26%

rr_ExpensesOverAssets

1.34%

^[6]

Net Annual Fund Operating Expenses After Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.02%

^[6]

rr_NetExpensesOverAssets

1.32%

^[6]

rr_ExpenseExampleByYearColumnName

Class A Shares

rr_ExpenseExampleYear01

704

rr_ExpenseExampleYear03

975

rr_ExpenseExampleYear05

1,267

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleYear10

2,095

rr_ExpenseExampleNoRedemptionByYearColumnName

Class A Shares

rr_ExpenseExampleNoRedemptionYear01

704

rr_ExpenseExampleNoRedemptionYear03

975

rr_ExpenseExampleNoRedemptionYear05

1,267

rr_ExpenseExampleNoRedemptionYear10

2,095

Perkins Small Cap Value Fund | Class A, C, S, I, R, T Shares | Class C

rr_RiskReturnAbstract

rr_OperatingExpensesColumnName

Class C

rr_ManagementFeesOverAssets

0.83%

rr_DistributionAndService12b1FeesOverAssets

1.00%

rr_OtherExpensesOverAssets

0.30%

rr_ExpensesOverAssets

2.13%

^[6]

Net Annual Fund Operating Expenses After Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

0.06%

^[6]

rr_NetExpensesOverAssets

2.07%

^[6]

rr_ExpenseExampleByYearColumnName

Class C Shares

rr_ExpenseExampleYear01

316

rr_ExpenseExampleYear03

667

rr_ExpenseExampleYear05

1,144

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleYear10

2,462

rr_ExpenseExampleNoRedemptionByYearColumnName

Class C Shares

rr_ExpenseExampleNoRedemptionYear01

216

rr_ExpenseExampleNoRedemptionYear03

667

rr_ExpenseExampleNoRedemptionYear05

1,144

rr_ExpenseExampleNoRedemptionYear10

2,462

Perkins Small Cap Value Fund | Class A, C, S, I, R, T Shares | Class S

rr_RiskReturnAbstract

rr_OperatingExpensesColumnName

Class S

rr_ManagementFeesOverAssets

0.83%

rr_DistributionAndService12b1FeesOverAssets

0.25%

rr_OtherExpensesOverAssets

0.30%

rr_ExpensesOverAssets

1.38%

^[6]

Net Annual Fund Operating Expenses After Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

none

^[6]

rr_NetExpensesOverAssets

1.38%

^[6]

rr_ExpenseExampleByYearColumnName

Class S Shares

rr_ExpenseExampleYear01

140

rr_ExpenseExampleYear03

437

rr_ExpenseExampleYear05

755

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleYear10

1,657

rr_ExpenseExampleNoRedemptionByYearColumnName

Class S Shares

rr_ExpenseExampleNoRedemptionYear01

140

rr_ExpenseExampleNoRedemptionYear03

437

rr_ExpenseExampleNoRedemptionYear05

755

rr_ExpenseExampleNoRedemptionYear10

1,657

Perkins Small Cap Value Fund | Class A, C, S, I, R, T Shares | Class I

rr_RiskReturnAbstract

rr_OperatingExpensesColumnName

Class I

rr_ManagementFeesOverAssets

0.83%

rr_DistributionAndService12b1FeesOverAssets

none

rr_OtherExpensesOverAssets

0.15%

rr_ExpensesOverAssets

0.98%

^[6]

Net Annual Fund Operating Expenses After Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

none

^[6]

rr_NetExpensesOverAssets

0.98%

^[6]

rr_ExpenseExampleByYearColumnName

Class I Shares

rr_ExpenseExampleYear01

100

rr_ExpenseExampleYear03

312

rr_ExpenseExampleYear05

542

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleYear10

1,201

rr_ExpenseExampleNoRedemptionByYearColumnName

Class I Shares

rr_ExpenseExampleNoRedemptionYear01

100

rr_ExpenseExampleNoRedemptionYear03

312

rr_ExpenseExampleNoRedemptionYear05

542

rr_ExpenseExampleNoRedemptionYear10

1,201

Perkins Small Cap Value Fund | Class A, C, S, I, R, T Shares | Class R

rr_RiskReturnAbstract

rr_OperatingExpensesColumnName

Class R

rr_ManagementFeesOverAssets

0.83%

rr_DistributionAndService12b1FeesOverAssets

0.50%

rr_OtherExpensesOverAssets

0.30%

rr_ExpensesOverAssets

1.63%

^[6]

Net Annual Fund Operating Expenses After Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

none

^[6]

rr_NetExpensesOverAssets

1.63%

^[6]

rr_ExpenseExampleByYearColumnName

Class R Shares

rr_ExpenseExampleYear01

166

rr_ExpenseExampleYear03

514

rr_ExpenseExampleYear05

887

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleYear10

1,933

rr_ExpenseExampleNoRedemptionByYearColumnName

Class R Shares

rr_ExpenseExampleNoRedemptionYear01

166

rr_ExpenseExampleNoRedemptionYear03

514

rr_ExpenseExampleNoRedemptionYear05

887

rr_ExpenseExampleNoRedemptionYear10

1,933

Perkins Small Cap Value Fund | Class A, C, S, I, R, T Shares | Class T

rr_RiskReturnAbstract

rr_OperatingExpensesColumnName

Class T

rr_ManagementFeesOverAssets

0.83%

rr_DistributionAndService12b1FeesOverAssets

none

rr_OtherExpensesOverAssets

0.30%

rr_ExpensesOverAssets

1.13%

^[6]

Net Annual Fund Operating Expenses After Fee Waiver

rr_FeeWaiverOrReimbursementOverAssets

none

^[6]

rr_NetExpensesOverAssets

1.13%

^[6]

rr_ExpenseExampleByYearColumnName

Class T Shares

rr_ExpenseExampleYear01

115

rr_ExpenseExampleYear03

359

rr_ExpenseExampleYear05

622

Expense Example, No Redemption, By Year, Column [Text]

rr_ExpenseExampleYear10

1,375

rr_ExpenseExampleNoRedemptionByYearColumnName

Class T Shares

rr_ExpenseExampleNoRedemptionYear01

115

rr_ExpenseExampleNoRedemptionYear03

359

rr_ExpenseExampleNoRedemptionYear05

622

rr_ExpenseExampleNoRedemptionYear10

1,375

2002

rr_AnnualReturn2002

(15.59%)

2003

rr_AnnualReturn2003

36.78%

2004

rr_AnnualReturn2004

13.57%

2005

rr_AnnualReturn2005

8.90%

2006

rr_AnnualReturn2006

12.37%

2007

rr_AnnualReturn2007

2.97%

2008

rr_AnnualReturn2008

(21.79%)

rr_AnnualReturn2009

36.59%

rr_AnnualReturn2010

17.87%

rr_AnnualReturn2011

(3.43%)

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended March 31, 2012 was 8.15%.

rr_BarChartYearToDateReturnDate

Mar. 31, 2012

rr_BarChartYearToDateReturn

8.15%

rr_HighestQuarterlyReturnLabel

Best Quarter:

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

rr_BarChartHighestQuarterlyReturn

23.04%

rr_LowestQuarterlyReturnLabel

Worst Quarter:

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2002

rr_BarChartLowestQuarterlyReturn

(22.57%)

Perkins Small Cap Value Fund | Class A, C, S, I, R, T Shares | Return Before Taxes | Class A

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class A Shares

rr_AverageAnnualReturnLabel

Return Before Taxes

^[2]

rr_AverageAnnualReturnYear01

(9.12%)

rr_AverageAnnualReturnYear05

3.17%

rr_AverageAnnualReturnYear10

6.34%

Perkins Small Cap Value Fund | Class A, C, S, I, R, T Shares | Return Before Taxes | Class C

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class C Shares

rr_AverageAnnualReturnLabel

Return Before Taxes

^[3]

rr_AverageAnnualReturnYear01

(5.21%)

rr_AverageAnnualReturnYear05

3.62%

rr_AverageAnnualReturnYear10

6.22%

Perkins Small Cap Value Fund | Class A, C, S, I, R, T Shares | Return Before Taxes | Class S

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class S Shares

rr_AverageAnnualReturnLabel

Return Before Taxes

rr_AverageAnnualReturnYear01

(3.69%)

rr_AverageAnnualReturnYear05

4.36%

rr_AverageAnnualReturnYear10

6.98%

Perkins Small Cap Value Fund | Class A, C, S, I, R, T Shares | Return Before Taxes | Class I

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class I Shares

rr_AverageAnnualReturnLabel

Return Before Taxes

rr_AverageAnnualReturnYear01

(3.28%)

rr_AverageAnnualReturnYear05

4.60%

rr_AverageAnnualReturnYear10

7.23%

Perkins Small Cap Value Fund | Class A, C, S, I, R, T Shares | Return Before Taxes | Class R

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class R Shares

rr_AverageAnnualReturnLabel

Return Before Taxes

rr_AverageAnnualReturnYear01

(3.89%)

rr_AverageAnnualReturnYear05

4.10%

rr_AverageAnnualReturnYear10

6.72%

Perkins Small Cap Value Fund | Class A, C, S, I, R, T Shares | Return Before Taxes | Class T

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class T Shares

rr_AverageAnnualReturnLabel

Return Before Taxes

rr_AverageAnnualReturnYear01

(3.43%)

rr_AverageAnnualReturnYear05

4.60%

rr_AverageAnnualReturnYear10

7.23%

Perkins Small Cap Value Fund | Class A, C, S, I, R, T Shares | Return After Taxes on Distributions | Class T

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class T Shares

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

rr_AverageAnnualReturnYear01

(5.87%)

rr_AverageAnnualReturnYear05

2.87%

rr_AverageAnnualReturnYear10

5.36%

Perkins Small Cap Value Fund | Class A, C, S, I, R, T Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class T

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class T Shares

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[4]

rr_AverageAnnualReturnYear01

(0.57%)

rr_AverageAnnualReturnYear05

3.41%

rr_AverageAnnualReturnYear10

5.73%

Perkins Small Cap Value Fund | Class A, C, S, I, R, T Shares | Russell 2000 Value Index (reflects no deduction for expenses, fees, or taxes)

rr_RiskReturnAbstract

rr_AverageAnnualReturnLabel

Russell 2000^® Value Index

rr_AverageAnnualReturnYear01

(5.50%)

rr_AverageAnnualReturnYear05

(1.87%)

rr_AverageAnnualReturnYear10

6.40%

Perkins Small Cap Value Fund | Class D Shares

rr_RiskReturnAbstract

jif_SupplementTextBlock

Janus Investment Fund

Perkins Small Cap Value Fund

Class D Shares

Supplement dated May 31, 2012

to Currently Effective Prospectuses

Effective May 31, 2012, the following replaces corresponding information for Perkins Small Cap Value Fund (the “Fund”).

1. The following replaces in its entirety the corresponding information found under “ANNUAL FUND OPERATING EXPENSES” in the Fund Summary section of the Fund’s Prospectus:



ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)							Class D

Management Fees (may adjust up or down)							0.83%
Other Expenses							0.20%
Total Annual Fund Operating Expenses⁽¹⁾							1.03%

(1)

Janus Capital has contractually agreed to waive the Fund’s total annual fund operating expenses (excluding any performance adjustments to management fees, administrative services fees payable pursuant to the Transfer Agency Agreement, brokerage commissions, interest, dividends, taxes, acquired fund fees and expenses, and extraordinary expenses) to 0.96% until at least November 1, 2012. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

2. The following replaces in its entirety the corresponding example table found under “EXAMPLE” in the Fund Summary section of the Fund’s Prospectus:


	1 Year		3 Years		5 Years		10 Years
Class D Shares	$	105	$	328	$	569	$	1,259

3. The following replaces in its entirety the corresponding information found under “PERFORMANCE INFORMATION” in the Fund Summary section of the Fund’s Prospectus:

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. Class D Shares of the Fund commenced operations on February 16, 2010, as a result of the restructuring of Class J Shares. The performance shown for Class D Shares for periods prior to February 16, 2010, reflects the performance of the Fund’s former Class J Shares (formerly named Investor Shares). For the periods prior to April 21, 2003, the performance shown for Class D Shares reflects the historical performance of Berger Small Cap Value Fund – Investor Shares (as a result of a prior reorganization of Berger Small Cap Value Fund – Investor Shares into the Fund’s Class J Shares). If Class D Shares of the Fund had been available during periods prior to February 16, 2010, the performance shown may have been different. The performance shown for periods following the Fund’s commencement of Class D Shares reflects the fees and expenses of Class D Shares, net of any applicable fee and expense limitations or waivers.



Annual Total Returns for Class D Shares (calendar year-end)

2002	2003	2004	2005	2006	2007	2008	2009	2010	2011
−15.59%	36.78%	13.57%	8.90%	12.37%	2.97%	−21.79%	36.59%	18.00%	−3.33%

Best Quarter: Second Quarter 2009 23.04% Worst Quarter: Third Quarter 2002 −22.57%

The Fund’s year-to-date return as of the calendar quarter ended March 31, 2012 was 8.15%.

Average Annual Total Returns (periods ended 12/31/11)

1 Year

5 Years

10 Years

Class D Shares

Return Before Taxes

−3.33%

4.64%

7.25%

Return After Taxes on Distributions

−5.81%

2.91%

5.38%

Return After Taxes on Distributions and Sale of Fund Shares⁽¹⁾

−0.51%

3.44%

5.75%

Russell 2000^® Value Index

−5.50%

−1.87%

6.40%

(reflects no deduction for expenses, fees, or taxes)


(1)	If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Please retain this Supplement with your records.

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

November 1, 2012

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceNarrativeTextBlock

rr_PerformanceInformationIllustratesVariabilityOfReturns

rr_PerformanceAdditionalMarketIndex

rr_PerformanceAvailabilityPhone

1-800-525-3713

rr_PerformanceAvailabilityWebSiteAddress

janus.com/allfunds

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

rr_BarChartHeading

Annual Total Returns for Class D Shares (calendar year-end)

rr_BarChartClosingTextBlock

Best Quarter: Second Quarter 2009 23.04% Worst Quarter: Third Quarter 2002 -22.57%

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

rr_PerformanceTableNotRelevantToTaxDeferred

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

rr_PerformanceTableNarrativeTextBlock

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/allfunds or by calling 1-800-525-3713.

Perkins Small Cap Value Fund | Class D Shares | Class D

rr_RiskReturnAbstract

rr_OperatingExpensesColumnName

Class D

rr_ManagementFeesOverAssets

0.83%

rr_OtherExpensesOverAssets

0.20%

rr_ExpensesOverAssets

1.03%

^[7]

rr_ExpenseExampleByYearColumnName

Class D Shares

rr_ExpenseExampleYear01

105

rr_ExpenseExampleYear03

328

rr_ExpenseExampleYear05

569

rr_ExpenseExampleYear10

1,259

2002

rr_AnnualReturn2002

(15.59%)

2003

rr_AnnualReturn2003

36.78%

2004

rr_AnnualReturn2004

13.57%

2005

rr_AnnualReturn2005

8.90%

2006

rr_AnnualReturn2006

12.37%

2007

rr_AnnualReturn2007

2.97%

2008

rr_AnnualReturn2008

(21.79%)

rr_AnnualReturn2009

36.59%

rr_AnnualReturn2010

18.00%

rr_AnnualReturn2011

(3.33%)

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended March 31, 2012 was 8.15%.

rr_BarChartYearToDateReturnDate

Mar. 31, 2012

rr_BarChartYearToDateReturn

8.15%

rr_HighestQuarterlyReturnLabel

Best Quarter:

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

rr_BarChartHighestQuarterlyReturn

23.04%

rr_LowestQuarterlyReturnLabel

Worst Quarter:

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2002

rr_BarChartLowestQuarterlyReturn

(22.57%)

Perkins Small Cap Value Fund | Class D Shares | Return Before Taxes | Class D

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class D Shares

rr_AverageAnnualReturnLabel

Return Before Taxes

rr_AverageAnnualReturnYear01

(3.33%)

rr_AverageAnnualReturnYear05

4.64%

rr_AverageAnnualReturnYear10

7.25%

Perkins Small Cap Value Fund | Class D Shares | Return After Taxes on Distributions | Class D

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class D Shares

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

rr_AverageAnnualReturnYear01

(5.81%)

rr_AverageAnnualReturnYear05

2.91%

rr_AverageAnnualReturnYear10

5.38%

Perkins Small Cap Value Fund | Class D Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class D

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class D Shares

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[4]

rr_AverageAnnualReturnYear01

(0.51%)

rr_AverageAnnualReturnYear05

3.44%

rr_AverageAnnualReturnYear10

5.75%

Perkins Small Cap Value Fund | Class D Shares | Russell 2000 Value Index (reflects no deduction for expenses, fees, or taxes) | Class D

rr_RiskReturnAbstract

rr_AverageAnnualReturnLabel

Russell 2000^® Value Index

rr_AverageAnnualReturnYear01

(5.50%)

rr_AverageAnnualReturnYear05

(1.87%)

rr_AverageAnnualReturnYear10

6.40%

Perkins Small Cap Value Fund | Class L Shares

rr_RiskReturnAbstract

jif_SupplementTextBlock

Janus Investment Fund

Perkins Small Cap Value Fund

Class L Shares

Supplement dated May 31, 2012

to Currently Effective Prospectuses

Effective May 31, 2012, the following replaces corresponding information for Perkins Small Cap Value Fund (the “Fund”).

1. The following replaces in its entirety the corresponding information found under “ANNUAL FUND OPERATING EXPENSES” in the Fund Summary section of the Fund’s Prospectus:



ANNUAL FUND OPERATING EXPENSES (expenses that you pay each year as a percentage of the value of your investment)							Class L

Management Fees (may adjust up or down)							0.83%
Other Expenses							0.28%
Total Annual Fund Operating Expenses⁽¹⁾							1.11%

(1)

Janus Capital has contractually agreed to waive the Fund’s total annual fund operating expenses (excluding any performance adjustments to management fees, administrative services fees payable pursuant to the Transfer Agency Agreement, brokerage commissions, interest, dividends, taxes, acquired fund fees and expenses, and extraordinary expenses) to 0.96% until at least November 1, 2012. The contractual waiver may be terminated or modified prior to this date only at the discretion of the Board of Trustees.

2. The following replaces in its entirety the corresponding example table found under “EXAMPLE” in the Fund Summary section of the Fund’s Prospectus:


	1 Year		3 Years		5 Years		10 Years
Class L Shares	$	113	$	353	$	612	$	1,352

3. The following replaces in its entirety the corresponding information found under “PERFORMANCE INFORMATION” in the Fund Summary section of the Fund’s Prospectus:



Annual Total Returns for Class L Shares (calendar year-end)

2002	2003	2004	2005	2006	2007	2008	2009	2010	2011
−15.33%	37.18%	13.80%	9.14%	12.57%	3.21%	−21.63%	36.91%	18.18%	−3.18%

Best Quarter: Second Quarter 2009 23.27% Worst Quarter: Third Quarter 2002 −22.47%

The Fund’s year-to-date return as of the calendar quarter ended March 31, 2012 was 8.21%.

Average Annual Total Returns (periods ended 12/31/11)

1 Year

5 Years

10 Years

Class L Shares

Return Before Taxes

−3.18%

4.85%

7.48%

Return After Taxes on Distributions

−5.68%

3.09%

5.58%

Return After Taxes on Distributions and Sale of Fund Shares⁽¹⁾

−0.43%

3.60%

5.93%

Russell 2000^® Value Index

−5.50%

−1.87%

6.40%

(reflects no deduction for expenses, fees, or taxes)


(1)	If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

Please retain this Supplement with your records.

Fee Waiver or Reimbursement over Assets, Date of Termination

rr_OperatingExpensesCaption

ANNUAL FUND OPERATING EXPENSES
(expenses that you pay each year as a percentage of the value of your investment)

rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination

November 1, 2012

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceNarrativeTextBlock

The following information provides some indication of the risks of investing in the Fund by showing how the Fund’s performance has varied over time. The performance shown for periods following April 21, 2003, reflects the fees and expenses of Class L Shares (formerly named Institutional Shares), net of any applicable fee and expense limitations or waivers. For the periods prior to April 21, 2003, the performance shown for Class L Shares reflects the historical performance of Berger Small Cap Value Fund – Institutional Shares (as a result of a prior reorganization of Berger Small Cap Value Fund – Institutional Shares into the Fund’s Class L Shares).

The bar chart depicts the change in performance from year to year during the periods indicated. The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions. For certain periods, the Fund’s performance reflects the effect of expense waivers. Without the effect of these expense waivers, the performance shown would have been lower.
The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future. Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

rr_PerformanceInformationIllustratesVariabilityOfReturns

rr_PerformanceAdditionalMarketIndex

The table compares the Fund’s average annual returns for the periods indicated to a broad-based securities market index. The index is not actively managed and is not available for direct investment. All figures assume reinvestment of dividends and distributions.

rr_PerformanceAvailabilityPhone

1-877-335-2687

rr_PerformanceAvailabilityWebSiteAddress

janus.com/advisor/mutual-funds

rr_PerformancePastDoesNotIndicateFuture

The Fund’s past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

rr_BarChartHeading

Annual Total Returns for Class L Shares (calendar year-end)

rr_BarChartClosingTextBlock

Best Quarter: Second Quarter 2009 23.27% Worst Quarter: Third Quarter 2002 -22.77%

rr_PerformanceTableHeading

Average Annual Total Returns (periods ended 12/31/11)

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historically highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.

rr_PerformanceTableNotRelevantToTaxDeferred

rr_PerformanceTableExplanationAfterTaxHigher

If the Fund incurs a loss, which generates a tax benefit, the Return After Taxes on Distributions and Sale of Fund Shares may exceed the Fund’s other return figures.

rr_PerformanceTableNarrativeTextBlock

rr_PerformanceTableClosingTextBlock

Updated performance information is available at janus.com/advisor/mutual-funds or by calling 1-877-335-2687.

Perkins Small Cap Value Fund | Class L Shares | Class L

rr_RiskReturnAbstract

rr_OperatingExpensesColumnName

Class L

rr_ManagementFeesOverAssets

0.83%

rr_OtherExpensesOverAssets

0.28%

rr_ExpensesOverAssets

1.11%

^[7]

rr_ExpenseExampleByYearColumnName

Class L Shares

rr_ExpenseExampleYear01

113

rr_ExpenseExampleYear03

353

rr_ExpenseExampleYear05

612

rr_ExpenseExampleYear10

1,352

2002

rr_AnnualReturn2002

(15.33%)

2003

rr_AnnualReturn2003

37.18%

2004

rr_AnnualReturn2004

13.80%

2005

rr_AnnualReturn2005

9.14%

2006

rr_AnnualReturn2006

12.57%

2007

rr_AnnualReturn2007

3.21%

2008

rr_AnnualReturn2008

(21.63%)

rr_AnnualReturn2009

36.91%

rr_AnnualReturn2010

18.18%

rr_AnnualReturn2011

(3.18%)

rr_YearToDateReturnLabel

The Fund’s year-to-date return as of the calendar quarter ended March 31, 2012 was 8.21%.

rr_BarChartYearToDateReturnDate

Mar. 31, 2012

rr_BarChartYearToDateReturn

8.21%

rr_HighestQuarterlyReturnLabel

Best Quarter:

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2009

rr_BarChartHighestQuarterlyReturn

23.27%

rr_LowestQuarterlyReturnLabel

Worst Quarter:

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2002

rr_BarChartLowestQuarterlyReturn

(22.47%)

Perkins Small Cap Value Fund | Class L Shares | Return Before Taxes | Class L

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class L Shares

rr_AverageAnnualReturnLabel

Return Before Taxes

rr_AverageAnnualReturnYear01

(3.18%)

rr_AverageAnnualReturnYear05

4.85%

rr_AverageAnnualReturnYear10

7.48%

Perkins Small Cap Value Fund | Class L Shares | Return After Taxes on Distributions | Class L

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class L Shares

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions

rr_AverageAnnualReturnYear01

(5.68%)

rr_AverageAnnualReturnYear05

3.09%

rr_AverageAnnualReturnYear10

5.58%

Perkins Small Cap Value Fund | Class L Shares | Return After Taxes on Distributions and Sale of Fund Shares | Class L

rr_RiskReturnAbstract

rr_AverageAnnualReturnColumnName

Class L Shares

rr_AverageAnnualReturnLabel

Return After Taxes on Distributions and Sale of Fund Shares

^[4]

rr_AverageAnnualReturnYear01

(0.43%)

rr_AverageAnnualReturnYear05

3.60%

rr_AverageAnnualReturnYear10

5.93%

Perkins Small Cap Value Fund | Class L Shares | Russell 2000 Value Index (reflects no deduction for expenses, fees, or taxes)

rr_RiskReturnAbstract

rr_AverageAnnualReturnLabel

Russell 2000^® Value Index

rr_AverageAnnualReturnYear01

(5.50%)

rr_AverageAnnualReturnYear05

(1.87%)