Lesions of heterotopic ossification were excised from thirty-seven joints in twenty-three adults who had had injuries to the brain. The lesions were excised from twenty-three elbows, twelve hips, and two shoulders. Patients were retrospectively divided into five categories according to the neural residua (cognitive and physical deficits). The patients in Class I (minimum cognitive and physical disability) and patients in Class II (minimum cognitive disability and moderate physical disability) who had fair or good selective control of the affected extremity had the best prognosis for maintaining the range of motion resulting from resecting the lesion and improving function postoperatively. They also had a low incidence of recurrence of the lesion. Seven of the nine elbows and eight of the eight hips in patients in these classes had successful results. All three of the patients in Class V (severe cognitive and physical deficits) who had a lesion of the hip and all eight of the patients in Class V with poor selective control had a poor result. In the twenty-five joints for which adequate follow-up radiographs were available to determine if the lesion recurred, fourteen recurrences were identified (56 per cent). Eleven of these patients were considered to have a poor result. Nine of the fourteen recurrences occurred in patients in Class V. Radiographic evidence of the maturity of the lesion and a normal level of alkaline phosphatase were of limited importance in predicting a low rate of recurrence. The over-all complications included four superficial infections and no instances of osteomyelitis.(ABSTRACT TRUNCATED AT 250 WORDS)