We retrospectively reviewed the five to ten-year results of an isolated proximal femoral osteotomy in two groups of patients. One group consisted of seventeen patients (eighteen hips) who had a residual deformity resulting from congenital dysplasia of the hip; there were fifteen women and two men, and the mean age was thirty-three years (range, twenty-four to fifty-eight years). The other group included sixteen patients (sixteen hips) who had idiopathic osteoarthrosis; there were three women and thirteen men, and the mean age was forty-eight years (range, thirty-eight to fifty-seven years). Both groups were evaluated clinically and radiographically, at a mean of 6.1 years (the patients who had residua of congenital dysplasia) and 6.7 years (the patients who had idiopathic osteoarthrosis).Of the seventeen patients who had residual deformity resulting from congenital dysplasia, eight (eight hips) were completely satisfied with the result of the osteotomy at least five years postoperatively; the joint space was improved in five of these patients (five hips) at the latest radiographic evaluation. Nine patients (ten hips) were not satisfied with the result of the osteotomy at the time of the most recent follow-up; four of them (four hips) had a subsequent total hip arthroplasty.Of the sixteen patients who had idiopathic osteoarthrosis, six were completely satisfied with the result of the osteotomy at least five years postoperatively. The joint space was improved in only two patients at the latest radiographic evaluation. The osteotomy did not provide lasting pain relief for seven patients, all of whom had a subsequent total hip arthroplasty.In both diagnostic groups, the most enduring clinical improvement occurred in hips that had the least evidence of osteoarthrotic changes on the preoperative radiographs. In addition, in the group that had residual deformity resulting from congenital dysplasia, the best outcomes were seen in hips with the least degree of acetabular dysplasia.