Exhibit 99.1

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 Results for Third Quarter of Fiscal 2005

Sixty-five percent year-over-year revenue growth driven by strong sales in Europe and North America

SEATTLE, WA—July 20, 2005—For the third quarter of fiscal 2005, F5 Networks announced revenue of $73.1 million, up 8 percent sequentially over revenue of $67.7 million in the second quarter and 65 percent over revenue of $44.2 million in the third quarter a year ago. Net income for the quarter was $14.0 million ($0.35 per diluted share), compared to $12.1 million ($0.31 per diluted share) in the prior quarter of fiscal 2005.

For the third quarter of fiscal 2004 the company reported net income of $7.4 million ($0.20 per diluted share). However, during the fourth quarter of 2004, F5 became subject to income taxes on U.S. income, and to present the results for prior periods on a tax-affected basis that is comparable to the current period, the company’s financial statements include pro forma earnings for the third quarter of fiscal 2004. On a pro forma basis, net income for the third quarter of fiscal 2004 would have been $4.9 million ($0.13 per diluted share) if the company had recorded a comparable provision for income taxes.

“During the third quarter, the company’s revenue growth reflected strong demand for our products in Europe and North America,” said John McAdam, F5 president and chief executive officer. “Compared to the prior quarter, revenue grew 19 percent in Europe and 25 percent in North America. Year over year, revenue in Europe and North America increased 78 percent and 69 percent respectively. The strength in these regions and solid performance in Asia-Pacific more than offset a slowdown in Japan that is typical of Japan’s first fiscal quarter.”

With continued revenue growth, stable gross margins, and further improvement in its expense ratio, the company’s operating margin was 27 percent in the third quarter, up from 16 percent in the third quarter of last year. Record cash flow of $21.2 million from operations contributed to a quarter-end balance of $329 million in cash and investments, a net increase of $36 million during the quarter.

F5 Networks Announces Fiscal Third Quarter Results

For the fourth quarter of fiscal 2005, ending September 30, McAdam said management has set a revenue target of $76 million to $78 million. Effective July 1, the company has voluntarily adopted the provisions of SFAS 123R, which would have required it to begin expensing the cost of stock-based compensation in the quarter beginning October 1. Accordingly, McAdam said, earnings for the fourth quarter are expected to be $0.29 to $0.30 per diluted share, including the charge for stock-based compensation. Excluding the compensation charge, the anticipated earnings range would have been $0.37 to $0.38 per diluted share. A reconciliation of the company’s expected GAAP and pro forma earnings is provided in the following table:

	Three months ended
	September 30, 2005
Reconciliation of Expected Pro Forma Fourth Quarter Earnings	Low	High
Net income Stock-based compensation expense, net of tax	$11,500 3,300	$11,900 3,300
Pro forma net income excluding stock compensation charges	$14,800	$15,200
Net income per share — diluted Pro forma net income per share — diluted	$0.29 $0.37	$0.30 $0.38

About F5 Networks

F5 enables organizations to successfully deliver business-critical applications and gives them the greatest level of agility to stay ahead of growing business demands. As the pioneer and global leader in Application Traffic Management, F5 continues to lead the industry by driving more intelligence into the network to deliver advanced application agility. F5 products ensure the secure and optimized delivery of applications to any user — anywhere. Through its flexible and cohesive architecture, F5 delivers unmatched value by dramatically improving the way organizations serve their employees, customers and constituents, while lowering operational costs. The company is headquartered in Seattle, Washington with offices worldwide. For more information go to www.f5.com.

Forward Looking Statements

Statements in this press release concerning revenue and earnings targets for the fourth quarter of fiscal 2005 and other statements that are not historical facts are forward-looking statements. Such forward-looking statements involve known and unknown risks, uncertainties and other factors which may 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, among others: customer acceptance of our new traffic management and security offerings; the timely development, introduction and acceptance of additional new products and features by F5 or its competitors; competitive pricing pressures; increased sales discounts; 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;

F5 Networks Announces Fiscal Third Quarter Results

and the unpredictability of F5’s sales cycle. F5 has no duty to update any guidance provided or other matters discussed in this press release. More information about potential risk factors that could affect F5’s business and financial results is included in the Company’s annual report on Form 10K for the fiscal year ended September 30, 2004, and other public filings with the Securities and Exchange Commission.

# # # #

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

	June 30,			September 30,
	2005			2004
Assets
Current assets
Cash and cash equivalents	$	11,587		$	24,901
Short-term investments		196,530			115,600
Restricted cash		2,400			—
Accounts receivable, net of allowances of $3,060 and $3,161		37,749			22,665
Inventories		2,288			1,696
Deferred tax assets		3,233			4,494
Other current assets		9,744			5,776
Total current assets		263,531			175,132
Restricted cash		3,875			6,243
Property and equipment, net		15,563			11,954
Long-term investments		120,962			81,792
Deferred tax assets		42,592			26,886
Goodwill		50,067			50,067
Other assets, net		8,856			8,279
Total assets	$	505,446		$	360,353
Liabilities and Shareholders’ Equity
Current liabilities
Accounts payable	$	6,201		$	4,840
Accrued liabilities		19,290			17,668
Deferred revenue		36,905			28,064
Total current liabilities		62,396			50,572
Long-term liabilities		2,701			2,136
Commitments and contingencies
Shareholders’ equity
Preferred Stock, no par value; 10,000 shares authorized, no shares outstanding		—			—
Common Stock, no par value; 100,000 shares authorized 38,387 and 34,772 shares issued and outstanding		403,641			306,655
Accumulated other comprehensive loss		(862	)		(498	)
Retained earnings		37,570			1,488
Total shareholders’ equity		440,349			307,645
Total liabilities and shareholders’ equity	$	505,446		$	360,353

F5 Networks, Inc.
Consolidated Income Statements
(unaudited, in thousands, except per share data)

	Three Months Ended				Nine Months Ended
	June 30,				June 30,
	2005		2004		2005		2004
Net revenues
Products	$	57,112	$	32,537	$	156,836	$	88,633
Services		15,952		11,706		43,967		32,338
Total		73,064		44,243		200,803		120,971
Cost of net revenues
Products		12,751		7,267		35,099		19,915
Services		4,306		2,832		11,600		7,920
Total		17,057		10,099		46,699		27,835
Gross profit		56,007		34,144		154,104		93,136
Operating expenses
Sales and marketing		23,207		16,907		63,732		47,781
Research and development		7,547		6,253		22,310		17,597
General and administrative		5,833		4,069		16,693		11,271
Amortization of unearned compensation		—		—		—		10
Total		36,587		27,229		102,735		76,659
Income from operations		19,420		6,915		51,369		16,477
Other income, net		2,123		848		5,151		1,840
Income before income taxes		21,543		7,763		56,520		18,317
Provision for income taxes		7,566		347		20,438		1,145
Net income	$	13,977	$	7,416	$	36,082	$	17,172
Net income per share – basic	$	0.37	$	0.22	$	0.98	$	0.52
Weighted average shares – basic		37,918		34,382		36,795		32,760
Net income per share – diluted	$	0.35	$	0.20	$	0.93	$	0.48
Weighted average shares – diluted		39,418		36,969		38,739		35,703

Reconciliation to pro forma results
Net income as reported	$	7,416	$	17,172
Provision for income taxes as reported		347		1,145
Income before income taxes		7,763		18,317
Pro forma 37% provision for income taxes		2,872		6,777
Pro forma net income	$	4,891	$	11,540
Pro forma net income per share – diluted	$	0.13	$	0.32
Pro forma weighted average shares – diluted		36,969		35,703