Nineteen spinal cord injury (SCI) patients were treated with resection of heterotopic ossification (HO) in 24 hips. The average follow-up period after surgery was 6.1 years. The mean time to surgery after injury was 50.6 months. The indication for surgery in all patients was improvement in hip motion to allow sitting. The average preoperative motion in flexion and extension was 11.5 degrees. The average intraoperative motion was 82.7 degrees. The average postoperative motion at the follow-up evaluation was 35.2 degrees. Fourteen of 19 patients (74%) had sufficient motion at the follow-up evaluation for sitting. Unlimited sitting tolerance was achieved in seven patients (37%), and seven patients (37%) had improved sitting posture with some time limitations. The average arc of motion in those patients able to sit at the follow-up evaluation was 41.5 degrees. Normal bone scans, alkaline phosphatase levels, and the mature roentgenographic appearance of HO were unreliable predictors of recurrence. The preoperative range of motion was the best predictor of improved postoperative range of motion since patients with retained motion did better than those with severe ankylosis. All six hips with severe recurrence had 0 degree of preoperative motion. The average degree of preoperative motion for all remaining hips was 15.3 degrees. The best predictor of recurrence was the roentgenographic grade of HO. Nineteen of 22 hips (86%) with a mild to severe recurrence had large amounts of bone preoperatively (Grades 3-5). Complications excluding recurrence occurred in 19 of 24 hips (79%) and included superficial wound infections in nine of 24 hips (38%) and deep persistent infections (osteomyelitis) in eight of 24 hips (33%).(ABSTRACT TRUNCATED AT 250 WORDS)