We treated eight patients who had complete rupture of the ischial origin of the hamstring muscles. This uncommon injury results from a sudden forceful flexion of the hip joint when the knee is extended and the hamstring muscles powerfully contracted. The injuries occurred during athletic exercise in six men and two women who had a mean age of 40 years (range, 22 to 53). With prompt diagnosis and surgery the final functional results in these patients were good. If the diagnosis is delayed, it is not possible to accomplish a primary suture of the hamstring muscles to the ischial bone. Consequently, another surgical procedure will need to be performed to restore function. Unlike cases of bony avulsion of the ischial apophysis in growing children, acute complete rupture of the proximal hamstring muscles origin in adults should be treated with prompt surgery.