Between May 1987 and October 1990, 21 constrained acetabular components were used in revision total hip arthroplasty at the University of California, San Francisco. In 18 patients, the device was placed for a chronically dislocating total hip arthroplasty. In the remaining three, intraoperative instability during revision total hip arthroplasty necessitated its use. At the minimum 2-year follow-up evaluation (average, 31 months; range, 24-64 months), 15 patients (71%) experienced no further dislocations or subluxations. There were eight dislocations in the remaining six patients (29%). The average Harris hip score at the follow-up evaluation was 76 points (range, 32-100 points). For those patients who redislocated (n = 6), an increased acetabular abduction angle of the metallic acetabular cup, averaging 70 degrees, was the only predictive factor of failure of the constrained cup (P < .05). No radiographic or clinical evidence of loosening in the 19 porous ingrowth acetabular component was observed. This device will relieve the complication of severe hip instability in the majority of patients, but is not universally successful.