On September 21, 1996, at 1047 eastern daylight time, a Mooney M20K, N3375X, was substantially damaged during a forced after takeoff from the Long Island Mac Arthur Airport (ISP), Islip, New York. The private pilot and passenger were not injured. Visual meteorological conditions prevailed for the personal flight that originated at ISP. No flight plan had been filed for the flight conducted under 14 CFR Part 91. In the NTSB Form 6120.1/2, the pilot stated he had refueled the airplane prior to the flight. After takeoff from runway 33L, during the landing gear retraction, the engine lost power. He then initiated a left turn back to the airport and completed a gear up landing. During an interview with the Federal Aviation Administration (FAA) Inspector, the pilot stated that the airplane had sat unused for 1 month, and had been refueled with 32.2 gallons of fuel before the takeoff. After takeoff, at 200 to 300 feet above the runway, the engine lost power and the pilot attempted a left turn to land on the taxiway parallel to runway 10. The airplane landed on the approach end of runway 10, heading in a westerly direction, and slid onto the grass between the taxiway and runway. The airplane came to rest on a heading of 230 degrees. On September 23, 1996, the pilot, also an FAA certified mechanic, arrived at the FAA Inspector's Office to present the airplane's maintenance log books for examination. After a review of the maintenance records by the FAA Inspector, the pilot voluntarily surrendered his medical and pilot certificates to the FAA Inspector. He also surrendered his airframe and powerplant mechanic, and inspection authorization certificates. The pilot stated that he had entered the airplane's annual inspection and signed it off the evening after the accident, and that he could not recall when the inspection was actually completed. Examination of the wreckage by the FAA Inspector revealed fuel in the airplane's fuel tanks, lines, and filter. Examination of the engine revealed valve train continuity, compression in all cylinders, and spark from the magnetos.