<PAGE>

                                          
                         SECURITIES AND EXCHANGE COMMISSION
                                          
                               WASHINGTON, D.C. 20549
                                          
                                    ___________
                                          
                                    Form 10-K/A

 /X/   ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE
       ACT OF 1934
                   FOR THE FISCAL YEAR ENDED DECEMBER 31, 1997, OR
 / /   TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES
       EXCHANGE ACT OF 1934

        FOR THE TRANSITION PERIOD FROM               TO                   .
                                          
                              COMMISSION FILE NUMBER:
                                          
                                --------------------
                                          
                                SYNC RESEARCH, INC.
                                          
               (Exact name of Registrant as specified in its charter)
                                          

                 DELAWARE                               33-0676350
     (State or other jurisdiction of                 (I.R.S. Employer
      incorporation or organization)               Identification No.)

                                      40 PARKER
                                   IRVINE, CA 92618

                       (Address of principal executive offices)

          Registrant's telephone number, including area code: (714) 588-2070

                                 -------------------

           Securities registered pursuant to Section 12(b) of the Act: None

             Securities registered pursuant to Section 12(g) of the Act:
                       Common Stock, $0.001 par value per share
                                   (Title of Class)

                                 -------------------

       Indicate by check mark whether the Registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
Registrant was required to file such reports) and (2) has been subject to such
filing requirements for the past 90 days. Yes /X/  No / /

       Indicate by check mark if disclosure of delinquent filers pursuant to
Item 405 of Regulation S-K is not contained herein, and will not be contained to
the best of Registrant's knowledge, in definitive proxy or information
statements incorporated by reference in Part III of this Form 10-K or any
amendment to this Form 10-K. / /

       The aggregate market value of the voting stock held by non-affiliates of
the Registrant based upon the closing sale price of the Registrant's Common
Stock on the Nasdaq National Market on March 13, 1998 was approximately
$57,544,019 as of such date. Shares of Common Stock held by each executive
officer and director and by each person who owns 10% or more of the outstanding
Common Stock have been excluded in that such persons may be deemed to be
affiliates. This determination of affiliate status is not necessarily a
conclusive determination for other purposes. 

       There were 17,367,197 shares of Registrant's Common Stock issued and
outstanding as of March 13, 1998.

                        DOCUMENTS INCORPORATED BY REFERENCE

       Part III incorporates information by reference from the definitive Proxy
Statement for the Registrant's 1998 Annual Meeting of Stockholders scheduled to
be held on June 12, 1998 (the "Proxy Statement").

--------------------------------------------------------------------------------
--------------------------------------------------------------------------------


<PAGE>

       
       The Registrant hereby amends the following item of its Form 10-K for the
fiscal year ended December 31, 1997 filed with the Securities and Exchange
Commission on March 31, 1998.

                                       PART II

ITEM 5.     MARKET FOR THE REGISTRANT'S COMMON STOCK AND RELATED
            STOCKHOLDER MATTERS

       The Company's Common Stock is listed on the Nasdaq Stock Market and 
trades under the symbol SYNX. The following table presents the high and low 
closing sale prices for the Company's Common Stock as reported in the Nasdaq 
National Market for the periods indicated. 

<TABLE>
<CAPTION>

                                     HIGH            LOW
                                     ----           -----
<S>                                 <C>            <C>
1997
   Q1 . . . . . . . . . . . . . .   $15.75          $3.03
   Q2 . . . . . . . . . . . . . .    $5.06          $2.25
   Q3 . . . . . . . . . . . . . .    $5.81          $3.00
   Q4 . . . . . . . . . . . . . .    $4.75          $3.00
   
1996
   Q1 . . . . . . . . . . . . . .   $44.38         $13.00
   Q2 . . . . . . . . . . . . . .   $22.25         $13.25
   Q3 . . . . . . . . . . . . . .   $17.13          $8.69
   Q4 . . . . . . . . . . . . . .   $19.63         $11.75

</TABLE>

     The Company had approximately 283 stockholders of record and 4,000 
beneficial shareholders as of March 13, 1998. 

     The Company has never paid cash dividends on its capital stock and does 
not intend to pay cash dividends on its capital stock in the foreseeable 
future. The Company's bank line of credit prohibits the Company from paying 
cash dividends without the bank's prior written consent. Any future 
determination to pay cash dividends will be at the discretion of the Board of 
Directors and will be dependent upon the Company's financial condition, 
results of operations, capital requirements and such other factors as the 
Board of Directors deems relevant.

USE OF PROCEEDS  

     In connection with its initial public offering in 1995, the Company 
filed a Registration Statement on Form S-1, SEC File No. 33-96910 (the 
"Registration Statement"), which was declared effective by the Commission on 
November 8, 1995. Pursuant to the Registration Statement, the Company 
registered and sold 2,585,000 shares of its Common Stock, $0.001 par value 
per share, for its own account. The offering was completed on November 9, 
1995. The aggregate offering price of the registered shares was $51,700,000. 
The managing underwriters of the offering were BancAmerica Robertson, 
Stephens (formerly Robertson, Stephens & Company), BT Alex. Brown (formerly 
Alex. Brown & Sons Incorporated) and Dian Rauscher Wessels (formerly Wessels,
Arnold & Henderson). 

     The Company incurred the following expenses in connection with the 
offering: 

<TABLE>
<S>                                                   <C>
Underwriting discounts and commissions . . . . . .   $    3,619,000
Other expenses . . . . . . . . . . . . . . . . . .          912,471
                                                      --------------
  Total Expenses . . . . . . . . . . . . . . . . .   $    4,531,471
                                                      --------------
                                                      --------------
</TABLE>

     All of such expenses were direct or indirect payments to others. 

     The net offering proceeds to the Company after deducting the total 
expenses above were $47,168,529. From November 9, 1995 to December 31, 1997, 
the Company used such net offering proceeds, in direct or indirect payments 
to others, as follows:  

<TABLE>
<S>                                                   <C>
Construction of plant, building and facilities . . . $      829,178
Purchase and installment of machinery and   
  equipment. . . . . . . . . . . . . . . . . . . . .      3,206,900
Acquisition of other business(es). . . . . . . . . .      5,338,000
Working capital. . . . . . . . . . . . . . . . . . .      4,328,453
Operating losses . . . . . . . . . . . . . . . . . .     22,698,047
                                                       -------------
  Total. . . . . . . . . . . . . . . . . . . . . . .    $36,400,578 (1)
                                                       -------------
                                                       -------------

</TABLE>

(1)  Excludes operating losses, capital expenditures and working capital changes
     of TyLink Corporation ("TyLink") prior to the Company's acquisition of
     TyLink in August 1996.

     In addition, the Company used aggregate proceeds of $316,292 to make 
payments to departing officers. This use of proceeds does not represent a 
material change in the use of proceeds described in the Registration 
Statement.

<PAGE>

                                      SIGNATURES

     Pursuant to the requirements of Section 13 or 15(d) of the Securities 
Exchange Act of 1934, the Registrant has duly caused this report to be signed 
on its behalf by the undersigned, thereunto duly authorized, in the City of 
Irvine, State of California, on May 1, 1998.

                               SYNC RESEARCH, INC.

                               By:      /s/ WILLIAM K. GUERRY
                              -------------------------------------------------
                                             William K. Guerry
                                   VICE PRESIDENT OF FINANCE AND ADMINISTRATION
                                        AND CHIEF FINANCIAL OFFICER 

     Pursuant to the requirements of the Securities Exchange Act of 1934, this
report has been signed by the following persons on behalf of the Registrant in 
the capacities and on the dates indicated: 

          SIGNATURE                     TITLE                         DATE
          ---------                     -----                         ----      
/s/ JOHN H. RADEMAKER*        Co-Chief Executive Officer, Vice   May 1, 1998
------------------------      Chairman of the Board    
   John H. Rademaker             


/s/ GREGORIO REYES*           Co-Chief Executive Officer,        May 1, 1998
------------------------      Chairman of the  Board   
   Gregorio Reyes      



/s/ WILLIAM K. GUERRY         Vice President of Finance and      May 1, 1998
------------------------      Administration, Secretary and 
   William K. Guerry          Chief Financial Officer  


/s/ CHARLES A. HAGGERTY*      Director                           May 1, 1998
------------------------      
   Charles A. Haggerty           


                              Director         
------------------------
   William J. Schroeder               


          
*By:  /s/ WILLIAM K. GUERRY        
---------------------------
      William K. Guerry
      (Attorney-in-Fact)