Table of Contents Washington, DC 20549 FORM 10-Q (Mark One) x QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended December 31, 2018 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 000-26251 NETSCOUT SYSTEMS, INC. UNITED STATES SECURITIES AND EXCHANGE COMMISSION (Exact Name of Registrant as Specified in Its Charter) (State or Other Jurisdict ...