UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Schedule 13D

Under the Securities Exchange Act of 1934

(Amendment No. 5)*

Duff & Phelps Corporation

(Name of Issuer)

Class A Common Stock, par value $0.01 per share

(Title of Class of Securities)

26433B107

(CUSIP Number)

Sander Levy

Vestar Capital Partners IV, L.P.

245 Park Avenue, 41st Floor

New York, New York 10167

(212) 351-1600

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

With a Copy to:

Christian O. Nagler

Kirkland & Ellis LLP

601 Lexington Avenue

New York, New York 10022

(212)446-4800

August 9, 2012

(Date of Event which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of Rule 13d-1(e), 13d-1(f) or 13d-1(g), check the following box.  ¨

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See Rule 13d-7 for other parties to whom copies are to be sent.

* The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

CUSIP No. 26433B107

1	NAME OF REPORTING PERSON Vestar Capital Partners IV, L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a)  ¨        (b)  ¨
3	SEC USE ONLY
4	SOURCE OF FUNDS*     OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2 (E)    ¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION     Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		7	SOLE VOTING POWER     0
		8	SHARED VOTING POWER     1,045,142*
		9	SOLE DISPOSITIVE POWER     0
		10	SHARED DISPOSITIVE POWER     1,045,142*
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON     1,045,142*
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*    ¨
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)     2.5%*
14	TYPE OF REPORTING PERSON*     PN

* See Item 5

CUSIP No. 26433B107

1	NAME OF REPORTING PERSON Vestar/D&P Holdings LLC
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a)  ¨        (b)  ¨
3	SEC USE ONLY
4	SOURCE OF FUNDS*     OO
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2 (E)    ¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION     Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		7	SOLE VOTING POWER     0
		8	SHARED VOTING POWER     31,875*
		9	SOLE DISPOSITIVE POWER     0
		10	SHARED DISPOSITIVE POWER     31,875*
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON     31,875*
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*    ¨
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)     0.1%
14	TYPE OF REPORTING PERSON*     OO

* See Item 5

CUSIP No. 26433B107

1	NAME OF REPORTING PERSON Vestar Associates IV, L.P.
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a)  ¨        (b)  ¨
3	SEC USE ONLY
4	SOURCE OF FUNDS*     Not applicable
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2 (E)    ¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION     Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		7	SOLE VOTING POWER     0
		8	SHARED VOTING POWER     1,045,142*
		9	SOLE DISPOSITIVE POWER     0
		10	SHARED DISPOSITIVE POWER     1,045,142*
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON     1,045,142*
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*    ¨
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)     2.5%
14	TYPE OF REPORTING PERSON*     PN

* See Item 5

CUSIP No. 26433B107

1	NAME OF REPORTING PERSON Vestar Associates Corporation IV
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP* (a)  ¨        (b)  ¨
3	SEC USE ONLY
4	SOURCE OF FUNDS*     Not applicable
5	CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEMS 2(D) OR 2(E)    ¨
6	CITIZENSHIP OR PLACE OF ORGANIZATION     Delaware
NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH		7	SOLE VOTING POWER     0
		8	SHARED VOTING POWER     1,045,142*
		9	SOLE DISPOSITIVE POWER     0
		10	SHARED DISPOSITIVE POWER     1,045,142*
11	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON     1,045,142*
12	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES*    ¨
13	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)     2.5%
14	TYPE OF REPORTING PERSON*     CO

* See Item 5

The Statement on Schedule 13D filed on October 15, 2007 (the “Original Schedule 13D”), as amended by Amendment No. 1 to the Original Schedule 13D filed on May 29, 2009 (“Amendment No. 1”), Amendment No. 2 to the Original Schedule 13D filed on March 6, 2012 (“Amendment No. 2”), Amendment No. 3 to the Original Schedule 13D filed on March 12, 2012 (“Amendment No. 3”) and Amendment No. 4 to the Original Schedule 13D filed on March 14, 2012 (“Amendment No. 4” and, together with the Original Schedule 13D, Amendment No. 1, Amendment No. 2 and Amendment No. 3, the “Schedule 13D”), by (i) Vestar Capital Partners IV, L.P. (“VCP IV”) and Vestar/D&P Holdings LLC (“V/D&P”, and together with VCP IV, the “Vestar Investors”) and (ii) Vestar Associates IV, L.P. (“VA IV”), the general partner of VCP IV, and Vestar Associates Corporation IV (“VAC IV”), the general partner of Vestar Associates IV, L.P. (“VA IV” and, together with the Vestar Investors and VAC IV, the “Reporting Persons”), relating to shares of Class A common stock, par value $0.01 per share (the “Common Stock”) of Duff & Phelps Corporation, a Delaware corporation (the “Issuer”), is hereby amended and supplemented as set forth below by this Amendment No. 5 to the Original Schedule 13D. Capitalized terms not defined herein have the meanings given to such terms in the Original Schedule 13D. Except as specifically provided herein, this Amendment No. 5 does not modify any of the information previously reported in the Schedule 13D.

Item 5. Interest in Securities of the Issuer.

Item 5 is hereby amended and restated in its entirety as follows:

The ownership percentages set forth below are based on 40,386,049 shares of the Issuer’s Common Stock outstanding, as set forth in the Issuer’s Prospectus Supplement (the “Prospectus”) filed pursuant to Rule 424(b)(5) on August 6, 2012 (File No. 333- 162551) (assuming no exercise of the underwriters’ over-allotment option in connection with the offering described therein). Beneficial ownership is determined in accordance with Rule 13d-3 under the Securities Exchange Act of 1934.

(a) On August 9, 2012, VCP IV and V/D&P exchanged 1,739,823 New Class A Units and 54,733 New Class A Units, respectively, together with an equivalent number of shares of Class B common stock of the Issuer for an equivalent number of shares of Common Stock, which were sold to Goldman, Sachs & Co. pursuant to the Underwriting Agreement (described below), in a registered public offering at a price per share of Common Stock equal to $13.25. As a result of their right to exchange New Class A Units for shares of Common Stock pursuant to the Exchange Agreement, VCP IV and V/D&P directly beneficially own 1,013,267 and 31,875 shares of Common Stock, respectively, for their own account, representing approximately 2.4% and 0.1%, respectively, of the total number of shares of Common Stock outstanding following exchange of their New Class A Units for shares of Common Stock. V/D&P is controlled by its managing member, VCP IV; VCP IV is controlled by its general partner, VA IV, and VA IV is controlled by its general partner, VAC IV. As a result, VCP IV, VA IV and VAC IV may be deemed to beneficially own the 1,045,142 shares of Common Stock owned by both VCP IV and V/D&P, representing approximately 2.5% of the total number of shares of Common Stock outstanding following exchange of their New Class A Units for shares of Common Stock. VCP IV, VA IV and VAC IV may be deemed to beneficially own the 1,045,142 shares of Class B Common Stock, which carry one vote per share, owned by both VCP IV and V/D&P, which, based on 2,157,082 shares of Class B Common Stock outstanding as set forth in the Prospectus, represents approximately 4.8% of the total number of shares of Common Stock and Class B Common Stock outstanding, considered together as a single class.

(b) The Reporting Persons have and will have the shared power to vote and dispose of the shares of Common Stock that they beneficially own, by virtue of the relationships described above.

(c) To the best knowledge of the Reporting Persons, except as described in this Item 5, none of the Reporting Persons or the individuals named in Schedule A to this Schedule 13D has effected a transaction in New Class A Units or shares of Common Stock during the past 60 days (other than transactions that may have been effected in the ordinary course of business in an agency or a fiduciary capacity).

(d) Other than the Reporting Persons, no other person is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of the Reporting Persons’ securities.

(e) Not applicable.

Item 6. Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer.

Item 6 is hereby supplemented to add the following:

On August 6, 2012, VCP IV and V/D&P entered into an underwriting agreement (the “Underwriting Agreement”) with the Issuer, another selling stockholder (collectively, with VCP IV and V/D&P, the “Selling Stockholders”) and Goldman, Sachs & Co., as underwriter (the “Underwriter”), with respect to the sale of Common Stock. Subject to certain conditions, the Underwriter agreed to purchase 3,000,000 shares of Common Stock from the Selling Stockholders.

The Underwriter was committed to take and pay for all of the shares of Common Stock being offered, if any were taken.

The Underwriter proposes to offer the shares of Common Stock from time to time for sale in one or more transactions on the New York Stock Exchange, in the over-the-counter market, through negotiated transactions or otherwise at market prices prevailing at the time of sale, at prices related to prevailing market prices or at negotiated prices, subject to receipt and acceptance by it and subject to its right to reject any order in whole or in part.

The Underwriter has an option to buy up to an additional 450,000 shares of Common Stock from the Selling Stockholders to cover sales by the Underwriter of more than 3,000,000 shares of Common Stock. The Underwriter may exercise that option for 30 days.

The description above is qualified in its entirety by reference to the Underwriting Agreement, which is filed as Exhibit 5 hereto and incorporated herein by reference.

Item 7. Material to Be Filed as Exhibits.

Exhibit 1	Joint Filing Agreement, dated October 12, 2007, among the Reporting Persons (incorporated by reference to Exhibit 1 to the Schedule 13D filed by the Reporting Persons on October 15, 2007).
Exhibit 5	Underwriting Agreement, dated August 6, 2012, among the Issuer, Selling Stockholders and the Underwriter (incorporated by reference to Exhibit 1.1 to the Current Report on Form 8-K filed by the Issuer with the Securities and Exchange Commission on August 9, 2012).

SIGNATURES

After reasonable inquiry and to the best of each of the undersigned’s knowledge and belief, each of the undersigned certify that the information set forth in this statement is true, complete and correct.

August 13, 2012

VESTAR CAPITAL PARTNERS IV, L.P.
By:	Vestar Associates IV, L.P.,
	its General Partner
By:	Vestar Associates Corporation IV,
	its General Partner
By:	/s/ Sander Levy
	Name:	Sander Levy
	Title:	Managing Director
VESTAR/D&P HOLDINGS LLC
By:	Vestar Capital Partners IV, L.P.,
	its General Partner
By:	Vestar Associates IV, L.P.,
	its General Partner
By:	Vestar Associates Corporation IV,
	its General Partner
By:	/s/ Sander Levy
	Name:	Sander Levy
	Title:	Managing Director
VESTAR ASSOCIATES IV, L.P.
By:	Vestar Associates Corporation IV;
	its General Partner
By:	/s/ Sander Levy
	Name:	Sander Levy
	Title:	Managing Director
VESTAR ASSOCIATES CORPORATION IV
By:	/s/ Sander Levy
	Name:	Sander Levy
	Title:	Managing Director

Index of Exhibits

Exhibit 1	Joint Filing Agreement, dated October 12, 2007, among the Reporting Persons (incorporated by reference to Exhibit 1 to the Schedule 13D filed by the Reporting Persons on October 15, 2007).
Exhibit 5	Underwriting Agreement, dated August 6, 2012, among the Issuer, Selling Stockholders and the Underwriter (incorporated by reference to Exhibit 1.1 to the Current Report on Form 8-K filed by the Issuer with the Securities and Exchange Commission on August 9, 2012).