The painful dislocated or subluxated hip in the patient with cerebral palsy presents a difficult problem in management. Twenty-three patients with cerebral palsy who had a painful subluxated or dislocated hip with degenerative changes were operated on at The Hospital for Special Surgery. Eight patients had a unilateral hip arthrodesis. Six had a successful arthrodesis initially, resulting in relief of pain and return to the preoperative functional level. A pseudarthrosis developed in two patients, but both had successful revision surgery, one by a second arthrodesis and the other by a total hip replacement. Thirteen of the fifteen patients with a total hip replacement were pain-free and functioning at a level consistent with their over-all involvement. One patient had migration of the greater trochanter and slight bending of the femoral component, with persistent pain. A second patient had progressive loosening of the femoral component over a period of seven years, but continued to walk with minimum pain. Two patients had a recurrent dislocation, one requiring revision of the femoral component and the other, of the acetabular component. We think that the presence of cerebral palsy, even in the patient with severe involvement, is not a contraindication for either a hip arthrodesis or a total hip replacement for a painful deformed or degenerated hip. These patients should be treated for the pain in the hip, and the presence of the underlying neuromuscular disorder should not deter the appropriate treatment. For unilateral hip disease in patients who are unable to walk and in young, active patients, we recommend hip fusion.(ABSTRACT TRUNCATED AT 250 WORDS)