Between 1969 and 1981, 20 acetabular augmentations were performed on 17 cerebral palsied patients with progressive hip instability. Average follow-up was 41.5 months, with a range from 24 to 147 months. Evaluation of results was based on assessment of hip stability, center edge (CE) angle, range of motion, and postoperative complications. Eighteen hips were rated good, one fair, and one poor. Stability was achieved in 19 hips. The CE angle was increased from a preoperative mean of -17 degrees to a follow-up mean of 50 degrees. There was no significant difference between preoperative and follow-up hip range of motion. The only complication encountered was a supracondylar femur fracture sustained after spica cast immobilization. Acetabular augmentation can be used effectively in the treatment of progressive hip instability in patients with cerebral palsy.