EXHIBIT 99.1

ADTRAN, Inc.

REPORTS RESULTS for the FIRST QUARTER 2016

and DECLARES QUARTERLY CASH DIVIDEND

HUNTSVILLE, AL.—April 12, 2016—ADTRAN, Inc. (NASDAQ:ADTN) reported results for the first quarter 2016. For the quarter, sales were $142,204,000 compared to $142,835,000 for the first quarter of 2015. Net income was $5,014,000 compared to $3,317,000 for the first quarter of 2015. Earnings per share, assuming dilution, were $0.10 compared to $0.06 for the first quarter of 2015. Non-GAAP earnings per share were $0.14 compared to $0.10 for the first quarter of 2015. The reconciliation between GAAP earnings per share, diluted, and non-GAAP earnings per share, diluted, is in the table provided.

ADTRAN Chief Executive Officer Tom Stanton stated, “ADTRAN delivered a solid performance this quarter resulting in earnings coming in ahead of initial expectations. Compared to the same period last year, Q1 domestic revenue was up over 39% with increases in both our products and services businesses. Improved gross margins and lower operating expenses helped us increase operating income over 181% versus Q1 of 2015. Longer term, we expect further improvement in the carrier environment as customers accelerate investments in upgrading their network infrastructure to meet customer demand.”

The Company also announced that its Board of Directors declared a cash dividend for the first quarter of 2016. The quarterly cash dividend is $0.09 per common share to be paid to holders of record at the close of business on April 28, 2016. The ex-dividend date is April 26, 2016 and the payment date is May 12, 2016.

As was previously announced, ADTRAN has changed it financial reporting segments as of the quarter ended March 31, 2016. The Company will now report its financial performance based on two new reportable segments – Network Solutions and Services & Support. ADTRAN will post supplemental information regarding revenues by operating segment and category under its new and former reporting structure for the fiscal quarter ended March 31, 2016, and recast financial segment information for the four quarters and full year for fiscal years 2014 and 2015, as if reported under the new operating reporting structure, on the Investor Relations page of its website at www.adtran.com.

The Company confirmed that its first quarter conference call will be held Wednesday, April 13, 2016 at 9:30 a.m. Central Time. This conference call will be web cast live through StreetEvents.com. To listen, simply visit the Investor Relations site at www.adtran.com or www.streetevents.com approximately 10 minutes prior to the start of the call and click on the conference call link provided.

An online replay of the conference call will be available for seven days at www.streetevents.com. In addition, an online replay of the conference call, as well as the text of the Company’s earnings release, will be available on the Investor Relations site at www.adtran.com for at least 12 months following the call.

ADTRAN, Inc. is a leading global provider of networking and communications equipment. ADTRAN’s products enable voice, data, video and Internet communications across a variety of network infrastructures. ADTRAN solutions are currently in use by service providers, private enterprises, government organizations, and millions of individual users worldwide. For more information, please visit www.adtran.com.

For more information, contact the company at 800 9ADTRAN (800 923-8726) or via email at info@adtran.com. On the Web, visit www.adtran.com.

This press release contains forward-looking statements which reflect management’s best judgment based on factors currently known. However, these statements involve risks and uncertainties, including the successful development and market acceptance of new products, the degree of competition in the market for such products, the product and channel mix, component costs, manufacturing efficiencies, and other risks detailed in our annual report on Form 10-K for the year ended December 31, 2015. These risks and uncertainties could cause actual results to differ materially from those in the forward-looking statements included in this press release.

CONTACT: Roger Shannon Senior Vice President & CFO 256-963-8775 INVESTOR SERVICES/ASSISTANCE: Gayle Ellis Investor Services 256-963-8220

1

Condensed Consolidated Balance Sheet

(Unaudited)

(In thousands)

	March 31, 2016		December 31, 2015
Assets
Cash and cash equivalents	$	91,609	$	84,550
Short-term investments		29,303		34,396
Accounts receivable, net		67,492		71,917
Other receivables		9,199		19,321
Inventory		92,107		91,533
Prepaid expenses and other current assets		13,096		10,145
Deferred tax assets, net		17,967		18,924
Total Current Assets		320,773		330,786
Property, plant and equipment, net		73,511		73,233
Deferred tax assets, net		18,878		18,091
Goodwill		3,492		3,492
Other assets		9,157		9,276
Long-term investments		195,683		198,026
Total Assets	$	621,494	$	632,904
Liabilities and Stockholders’ Equity
Accounts payable	$	42,635	$	48,668
Unearned revenue		18,683		16,615
Accrued expenses		13,513		12,108
Accrued wages and benefits		11,064		12,857
Income tax payable, net		2,739		2,395
Total Current Liabilities		88,634		92,643
Non-current unearned revenue		7,288		7,965
Other non-current liabilities		25,283		24,236
Bonds payable		27,900		27,900
Total Liabilities		149,105		152,744
Stockholders’ Equity		472,389		480,160
Total Liabilities and Stockholders’ Equity	$	621,494	$	632,904

2

Consolidated Statements of Income

(Unaudited)

(In thousands, except per share data)

	Three Months Ended
	March 31,
	2016			2015
Sales
Products	$	123,883		$	129,505
Services		18,321			13,330
Total sales		142,204			142,835
Cost of sales
Products		64,073			71,560
Services		12,337			5,712
Total cost of sales		76,410			77,272
Gross Profit		65,794			65,563
Selling, general and administrative expenses		30,785			31,064
Research and development expenses		29,488			32,536
Operating Income		5,521			1,963
Interest and dividend income		855			933
Interest expense		(145	)		(148	)
Net realized investment gain		1,728			3,115
Other income (expense), net		119			(353	)
Income before provision for income taxes		8,078			5,510
Provision for income taxes		(3,064	)		(2,193	)
Net Income	$	5,014		$	3,317
Weighted average shares outstanding - basic		49,220			53,399
Weighted average shares outstanding - diluted (1)		49,389			53,634
Earnings per common share - basic	$	0.10		$	0.06
Earnings per common share - diluted (1)	$	0.10		$	0.06

⁽¹⁾  Assumes exercise of dilutive stock options calculated under the treasury stock method.

3

Consolidated Statements of Comprehensive Income

(Unaudited)

(In thousands)

	Three Months Ended
	March 31,
	2016			2015
Net Income	$	5,014		$	3,317
Other Comprehensive Income (Loss), net of tax:
Unrealized losses on available-for-sale securities		(255	)		(503	)
Defined benefit plan adjustments		45			68
Foreign currency translation		1,228			(3,318	)
Other Comprehensive Income (Loss), net of tax		1,018			(3,753	)
Comprehensive Income (Loss), net of tax	$	6,032		$	(436	)

4

Consolidated Statements of Cash Flows

(Unaudited)

(In thousands)

	Three Months Ended
	March 31,
	2016			2015
Cash flows from operating activities:
Net income	$	5,014		$	3,317
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization		3,347			3,728
Amortization of net premium on available-for-sale investments		220			910
Net realized gain on long-term investments		(1,728	)		(3,115	)
Net loss on disposal of property, plant and equipment		3			8
Stock-based compensation expense		1,558			1,639
Deferred income taxes		435			(692	)
Tax benefit from stock option exercises		—			8
Excess tax benefits from stock-based compensation arrangements		—			(9	)
Change in operating assets and liabilities:
Accounts receivable, net		4,752			(4,571	)
Other receivables		10,200			511
Inventory		163			(7,261	)
Prepaid expenses and other assets		(3,083	)		(736	)
Accounts payable		(6,520	)		20,084
Accrued expenses and other liabilities		902			(282	)
Income tax payable, net		413			(524	)
Net cash provided by operating activities		15,676			13,015
Cash flows from investing activities:
Purchases of property, plant and equipment		(3,166	)		(2,442	)
Proceeds from sales and maturities of available-for-sale investments		60,586			58,075
Purchases of available-for-sale investments		(52,053	)		(44,584	)
Net cash provided by investing activities		5,367			11,049
Cash flows from financing activities:
Proceeds from stock option exercises		247			280
Purchases of treasury stock		(11,003	)		(3,035	)
Dividend payments		(4,453	)		(4,811	)
Excess tax benefits from stock-based compensation arrangements		—			9
Net cash used in financing activities		(15,209	)		(7,557	)
Net increase in cash and cash equivalents		5,834			16,507
Effect of exchange rate changes		1,225			(2,937	)
Cash and cash equivalents, beginning of period		84,550			73,439
Cash and cash equivalents, end of period	$	91,609		$	87,009
Supplemental disclosure of non-cash investing activities
Purchases of property, plant and equipment included in accounts payable	$	485		$	784

5

Supplemental Information

Stock-based Compensation Expense

(Unaudited)

(In thousands)

	Three Months Ended
	March 31,
	2016			2015
Stock-based compensation expense included in cost of sales	$	91		$	90
Selling, general and administrative expense		810			691
Research and development expense		657			858
Stock-based compensation expense included in operating expenses		1,467			1,549
Total stock-based compensation expense		1,558			1,639
Tax benefit for expense associated with non-qualified options		(212	)		(180	)
Total stock-based compensation expense, net of tax	$	1,346		$	1,459

6

Reconciliation of GAAP net income per share, diluted, to

Non-GAAP net income per share, diluted

(Unaudited)

	Three Months Ended March 31,
	2016		2015
GAAP earnings per common share – diluted	$	0.10	$	0.06
Amortization of acquired intangible assets		0.01		0.01
Stock-based compensation expense		0.03		0.03
Non-GAAP earnings per common share – diluted	$	0.14	$	0.10

7