12 cases of Thompson's quadricepsplasty for extra-articular ankylosis of the knee joints which we experienced, were evaluated and analyzed. We obtained the following results. 1. Most of our cases had fracture in the middle one third of the femur. 2. Average 62.5 degrees of flexion range was gained by the operation. 3. Among the 2 cases in which extension lag existed before the operation, it has disappeared in one and still remained in the other case after the operation. 4 cases of new extension lags appeared after the operation. Average extension lag after the operation was 13 degrees. 4. Immediate postoperative exercises and adequate physiotherapy are considered to be very important.