Exhibit 99.1

4Q10/FY10 Earnings Release Page 1 of 5

FOR IMMEDIATE RELEASE

CONTACT:	Investor Relations
	John Eldridge
	(206) 272-6571
	j.eldridge@f5.com
	Public Relations
	Alane Moran
	(206) 272-6850
	a.moran@f5.com

F5 Networks Announces Fourth Quarter and Fiscal 2010 Results

Strong product sales drive quarterly revenue up 10 percent sequentially, 45 percent year over year

SEATTLE, WA—October 26, 2010—F5 Networks, Inc. (NASDAQ: FFIV) today announced revenue of $254.3 million for the fourth quarter of fiscal year 2010, up 10 percent from $230.5 million in the prior quarter and 45 percent from $175.1 million in the fourth quarter of fiscal year 2009. For fiscal year 2010, revenue was $882.0 million, up 35 percent from $653.1 million in fiscal year 2009.

GAAP net income for the fourth quarter was $48.2 million ($0.59 per diluted share) compared to $40.5 million ($0.50 per diluted share) in the third quarter of 2010 and $28.4 million ($0.36 per diluted share) in the fourth quarter a year ago. GAAP net income for the year was $151.2 million ($1.86 per diluted share) versus $91.5 million ($1.14 per diluted share) in fiscal year 2009.

Excluding the impact of stock-based compensation and a one-time charge related to a legal settlement, non-GAAP net income for the fourth quarter was $63.9 million ($0.79 per diluted share), compared to $53.3 million ($0.66 per diluted share) in the prior quarter and $40.0 million ($0.50 per diluted share) in the fourth quarter of fiscal 2009. For fiscal year 2010, non-GAAP net income was $203.8 million ($2.51 per diluted share) versus $134.6 million ($1.68 per diluted share) in fiscal year 2009.

A reconciliation of GAAP net income to non-GAAP net income is included on the attached Consolidated Statements of Operations.

F5 president and chief executive officer John McAdam said that during the fourth quarter the company continued to benefit from several key trends that drove demand for its products throughout fiscal 2010. “As enterprises and other large organizations confront the new realities of today’s global economy, they are turning increasingly to technologies that enable them to operate more efficiently and compete more successfully by giving them flexible, on-demand access to more resources while reducing overall costs. This shift is reflected broadly in the trend towards data center consolidation and the widespread adoption of server virtualization and new infrastructure models such as cloud computing.

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“Within the past year, these trends have accelerated, and our products have been increasingly deployed as strategic points of control in new data center architectures, integrating disparate resources and managing the flow of traffic within and between data centers. In addition, we have continued to see growing demand for our products among service providers grappling with the proliferation of mobile devices, the explosion of mobile applications and the corresponding increase in mobile data traffic. As a result, our product revenues grew 12 percent sequentially in Q4 and 38 percent during fiscal 2010,” said McAdam.

During the fourth quarter, further improvement in gross margins combined with strong revenue growth to drive the company’s GAAP operating margin to 30 percent and the non-GAAP operating margin to just under 38 percent.

On the company’s balance sheet, deferred revenue grew 8 percent sequentially to $259.4 million, up nearly 42 percent from the fourth quarter of fiscal 2009. Cash flow from operations was $86 million in the fourth quarter and $314 million for the full year. After repurchasing $75 million of F5 common stock in fiscal 2010, the company ended the year with $862 million in cash and investments.

“In general, Q4 was a strong finish to a strong year,” McAdam said. “Barring another broad economic setback, the strength of our current business and our growing pipeline are encouraging signs that the positive trends that drove our business in fiscal 2010 will continue through fiscal 2011.”

For the first quarter of fiscal 2011, ending December 31, the company has set a revenue target of $265 million to $270 million and a GAAP earnings target of $0.62 to $0.64 per diluted share. Excluding stock-based compensation expense, our non-GAAP earnings target is $0.80 to $0.82 per diluted share.

A reconciliation of the company’s expected GAAP and non-GAAP earnings is provided in the following table:

	Three months ended
	December 31, 2010
Reconciliation of Expected Non-GAAP First Quarter Earnings	Low		High
Net income	$	50.7	$	52.3
Stock-based compensation expense, net of tax		14.6		14.6
Non-GAAP net income excluding stock-based compensation expense	$	65.3	$	66.9
Net income per share — diluted	$	0.62	$	0.64
Non-GAAP net income per share — diluted	$	0.80	$	0.82

Share Repurchase Program

The company also announced today that its board of directors approved a new program to repurchase up to $200 million of the company’s outstanding common stock.

4Q10/FY10 Earnings Release Page 3 of 5

Acquisitions for the share repurchase program will be made from time to time in private transactions or open market purchases as permitted by securities laws and other legal requirements. The program may be modified or discontinued at any time.

Analyst/Investor Meeting

F5 will hold a meeting for analysts and investors at the Sofitel Hotel in New York City, from 8:00 a.m. to noon Eastern Time on Tuesday, November 16, 2010.

To register online, please visit: https://www.f5.com/about/investor-relations/analyst-meeting/

For more information contact Darlene Henderson (206.272.6170) or email 2010AIM@f5.com.

The meeting will also be webcast live and an archived version will be available through January 21, 2011. The link for the live webcast and the archived version is http://www.f5.com/about/investor-relations/events-calendar.html.

About F5 Networks

F5 Networks is the global leader in Application Delivery Networking (ADN), focused on ensuring the secure, reliable, and fast delivery of applications. F5’s flexible architectural framework enables community-driven innovation that helps organizations enhance IT agility and dynamically deliver services that generate true business value. F5’s vision of unified application and data delivery offers customers an unprecedented level of choice in how they deploy ADN solutions. It redefines the management of application, server, storage, and network resources, streamlining application delivery and reducing costs. Global enterprise organizations, service and cloud providers, and Web 2.0 content providers trust F5 to keep their business moving forward. For more information, go to www.f5.com.

Forward Looking Statements

Statements in this press release concerning the continuing strength of F5’s business, sequential growth, the target revenue and earnings range, share amount and share price assumptions, demand for application delivery networking and storage virtualization products and other statements that are not historical facts are forward-looking statements. Such forward-looking statements involve risks and uncertainties, as well as assumptions and other factors that, if they do not fully materialize or prove correct, could cause the actual results, performance or achievements of the company, or industry results, to be materially different from any future results, performance or achievements expressed or implied by such forward-looking statements. Such factors include, but are not limited to: customer acceptance of our new traffic management, security, application delivery, WAN optimization and storage virtualization offerings; the timely development, introduction and acceptance of additional new products and features by F5 or its competitors; competitive pricing pressures; increased sales discounts; uncertain global economic conditions which may result in reduced customer demand for our

4Q10/FY10 Earnings Release Page 4 of 5

products and services and changes in customer payment patterns; F5’s ability to sustain, develop and effectively utilize distribution relationships; F5’s ability to attract, train and retain qualified product development, marketing, sales, professional services and customer support personnel; F5’s ability to expand in international markets; the unpredictability of F5’s sales cycle; the share repurchase program; future prices of F5’s common stock; and other risks and uncertainties described more fully in our documents filed with or furnished to the Securities and Exchange Commission. All forward-looking statements in this press release are based on information available as of the date hereof and qualified in their entirety by this cautionary statement. F5 assumes no obligation to revise or update these forward-looking statements.

GAAP to non-GAAP Reconciliation

F5’s management evaluates and makes operating decisions using various operating measures. These measures are generally based on the revenues of its products, services operations and certain costs of those operations, such as cost of revenues, research and development, sales and marketing and general and administrative expenses. One such measure is net income excluding stock-based compensation, which is a non-GAAP financial measure under Section 101 of Regulation G under the Securities Exchange Act of 1934, as amended. This measure consists of GAAP net income excluding, as applicable, stock-based compensation. Net income excluding stock-based compensation (non-GAAP) is adjusted by the amount of additional taxes or tax benefit that the company would accrue if it used non-GAAP results instead of GAAP results to calculate the company’s tax liability. Stock-based compensation is a non-cash expense that F5 has accounted for since July 1, 2005 in accordance with the fair value recognition provisions of Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 718 Compensation – Stock Compensation (“FASB ASC Topic 718”).

Management believes that net income excluding stock-based compensation (non-GAAP) provides useful supplemental information to management and investors regarding the performance of the company’s business operations and facilitates comparisons to the company’s historical operating results. Although F5’s management finds this non-GAAP measure to be useful in evaluating the performance of the business, management’s reliance on this measure is limited because items excluded from such measures could have a material effect on F5’s earnings and earnings per share calculated in accordance with GAAP. Therefore, F5’s management will use its non-GAAP earnings and earnings per share measures, in conjunction with GAAP earnings and earnings per share measures, to address these limitations when evaluating the performance of the company’s business. Investors should consider these non-GAAP measures in addition to, and not as a substitute for, financial performance measures in accordance with GAAP.

The reconciliation of the company’s GAAP and non-GAAP earnings for the three months and twelve months ended September 30, 2010 also excludes a legal settlement charge.

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F5 believes that presenting its non-GAAP measure of earnings and earnings per share provides investors with an additional tool for evaluating the performance of the company’s business and which management uses in its own evaluation of the company’s performance. Investors are encouraged to look at GAAP results as the best measure of financial performance. For example, stock-based compensation is an obligation of the company that should be considered and each line item is important to financial performance generally. However, while the GAAP results are more complete, the company provides investors this supplemental measure since, with reconciliation to GAAP, it may provide additional insight into its operational performance and financial results.

###

F5 Networks, Inc.
Condensed Consolidated Balance Sheets
(unaudited, in thousands)

	September 30,			September 30,
	2010			2009
Assets
Current assets
Cash and cash equivalents	$	168,754		$	110,837
Short-term investments		259,742			206,291
Accounts receivable, net of allowances of $4,319 and $3,651		112,132			106,973
Inventories		18,815			13,819
Deferred tax assets		8,767			8,010
Other current assets		37,745			22,252
Total current assets		605,955			468,182
Restricted cash		195			2,729
Property and equipment, net		34,157			39,371
Long-term investments		433,570			257,294
Deferred tax assets		37,864			49,018
Goodwill		234,700			231,883
Other assets, net		15,751			20,168
Total assets	$	1,362,192		$	1,068,645
Liabilities and Shareholders’ Equity
Current liabilities
Accounts payable	$	21,180		$	18,891
Accrued liabilities		61,768			53,232
Deferred revenue		204,137			150,891
Total current liabilities		287,085			223,014
Other long-term liabilities		16,153			14,373
Deferred revenue, long-term		55,256			32,238
Total long-term liabilities		71,409			46,611
Commitments and contingencies
Shareholders’ equity
Preferred stock, no par value; 10,000 shares authorized, no shares outstanding		—			—
Common stock, no par value; 200,000 shares authorized 80,355 and 78,325 shares issued and outstanding		517,215			462,786
Accumulated other comprehensive loss		(3,241	)		(2,337	)
Retained earnings		489,724			338,571
Total shareholders’ equity		1,003,698			799,020
Total liabilities and shareholders’ equity	$	1,362,192		$	1,068,645

F5 Networks, Inc.
Condensed Consolidated Statements of Operations
(unaudited, in thousands, except per share amounts)

	Three Months Ended				Twelve Months Ended
	September 30,				September 30,
	2010		2009		2010		2009
Net revenues
Products	$	164,972	$	108,880	$	561,142	$	406,529
Services		89,302		66,250		320,830		246,550
Total		254,274		175,130		881,972		653,079
Cost of net revenues (1)
Products		31,045		24,294		113,834		95,209
Services		15,783		12,162		58,118		47,517
Total		46,828		36,456		171,952		142,726
Gross Profit		207,446		138,674		710,020		510,353
Operating expenses (1)
Sales and marketing		80,696		58,395		293,201		225,193
Research and development		31,571		25,515		118,314		103,664
General and administrative		18,876		14,619		68,503		55,243
Restructuring charges		—		—		—		4,329
Total		131,143		98,529		480,018		388,429
Income from operations		76,303		40,145		230,002		121,924
Other income, net		68		1,682		7,625		9,724
Income before income taxes		76,371		41,827		237,627		131,648
Provision for income taxes (1)		28,136		13,477		86,474		40,113
Net Income	$	48,235	$	28,350	$	151,153	$	91,535
Net income per share — basic	$	0.60	$	0.36	$	1.90	$	1.16
Weighted average shares — basic		80,268		78,499		79,609		78,842
Net income per share — diluted	$	0.59	$	0.36	$	1.86	$	1.14
Weighted average shares — diluted		81,253		79,613		81,049		80,073
Non-GAAP Financial Measures
Net income as reported	$	48,235	$	28,350	$	151,153	$	91,535
Stock-based compensation expense, net of tax (4)		14,702		11,696		51,675		39,190
Restructuring charges, net of tax (2)		—		—		—		2,957
Legal settlement, net of tax (3)		950		—		950		913
Net income excluding stock-based compensation, restructuring charges & legal settlement (non-GAAP)	$	63,887	$	40,046	$	203,778	$	134,595
Net income per share excluding stock-based compensation, restructuring charges & legal settlement (non-GAAP) — diluted	$	0.79	$	0.50	$	2.51	$	1.68
Weighted average shares — diluted		81,253		79,613		81,049		80,073

(1)	Includes stock-based compensation as follows:
	Cost of net revenues	$	2,002		$	1,472		$	7,063		$	5,152
	Sales and marketing		7,565			6,125			27,250			22,644
	Research and development		5,224			4,468			19,421			16,666
	General and administrative		4,991			3,272			17,039			11,602
	Tax effect of stock-based compensation		(5,080	)		(3,641	)		(19,098	)		(16,874	)
		$	14,702		$	11,696		$	51,675		$	39,190
(2)	Includes restructuring charges as follows:
	Loss on facility exit	$	—		$	—		$	—		$	2,194
	Restructuring charges		—			—			—			2,135
	Tax effect of loss on facility exit and restructuring charges		—			—			—			(1,372	)
		$	—		$	—		$	—		$	2,957
(3)	Includes legal settlement as follows:
	Legal settlement	$	1,500		$	—		$	1,500		$	1,337
	Tax effect of legal settlement		(550	)		—			(550	)		(424	)
		$	950		$	—		$	950		$	913
(4)	Stock-based compensation is accounted for in accordance with the fair value recognition provisions of Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 718, Compensation – Stock Compensation (“FASB ASC Topic 718”)

F5 Networks, Inc.
Condensed Consolidated Statements of Cash Flows
(unaudited, in thousands)

	Years ended
	September 30,
	2010			2009
Operating activities
Net income	$	151,153		$	91,535
Adjustments to reconcile net income to net cash provided by operating activities:
Realized gain on disposition of assets and investments		(125	)		(9	)
Stock-based compensation		70,773			56,064
Provisions for doubtful accounts and sales returns		1,206			2,638
Depreciation and amortization		23,833			26,407
Deferred income taxes		8,243			(6,057	)
Gain on auction rate securities put option		(1,491	)		(3,901	)
Loss on trading auction rate securities		1,491			3,901
Changes in operating assets and liabilities, net of amounts acquired:
Accounts receivable		(6,365	)		(12,555	)
Inventories		(4,996	)		(3,671	)
Other current assets		(17,064	)		(523	)
Other assets		(1,466	)		(226	)
Accounts payable and accrued liabilities		12,157			10,248
Deferred revenue		76,263			38,130
Net cash provided by operating activities		313,612			201,981
Investing activities
Purchases of investments		(877,003	)		(414,857	)
Sales and maturities of investments		648,875			328,110
Investment of restricted cash		2,530			13
Acquisition of intangible assets		—			(706	)
Purchases of property and equipment		(12,625	)		(11,669	)
Net cash used in investing activities		(238,223	)		(99,109	)
Financing activities
Excess tax benefits from share-based compensation		26,532			(1,958	)
Proceeds from the exercise of stock options and purchases of stock under employee stock purchase plan		31,670			18,688
Repurchase of common stock		(75,000	)		(87,436	)
Net cash used in financing activities		(16,798	)		(70,706	)
Net increase in cash and cash equivalents		58,591			32,166
Effect of exchange rate changes on cash and cash equivalents		(674	)		368
Cash and cash equivalents, beginning of period		110,837			78,303
Cash and cash equivalents, end of period	$	168,754		$	110,837