A consecutive series of seventy-six patients (101 hips) underwent primary open reduction, capsulorrhaphy, and innominate osteotomy for late-presenting developmental dislocation of the hip. They were between 1.5 and five years old at the time of surgery, which was done between 1958 and 1965. The present study was designed to review the outcome of these patients into middle age. We located and reviewed the cases of sixty patients (eighty hips), which represents a 79% rate of follow-up at forty to forty-eight years postoperatively. Nineteen patients (twenty-four hips) had undergone total hip replacement, and three (three hips) had died of unrelated causes. The remaining thirty-eight patients (fifty-three hips) were assessed by the WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index) and Oxford hip score questionnaires, physical examination, and a standing anteroposterior pelvic radiograph. The radiographs were analyzed to determine the minimum joint space width and the Kellgren and Lawrence score. Accepted indices of hip dysplasia were measured. With use of Kaplan-Meier survival analysis and with the end point defined as total hip replacement, the survival rates at thirty, forty, and forty-five years after the reduction were 99% (95% confidence interval, +/-2.4%), 86% (95% confidence interval, +/-6.9%), and 54% (95% confidence interval, +/-16.4%), respectively. The average Oxford hip score and WOMAC score for the surviving hips were 16.8 (range, 0 to 82) and 16.7 (range, 0 to 71), respectively. Of the fifty-one hips for which radiographs were available, thirty-eight demonstrated a minimum joint space width of >2.0 mm and thirteen demonstrated definite osteoarthritis on the basis of this criterion. Osteoarthritis, according to the system of Kellgren and Lawrence, was grade 0 or 1 in twenty-nine hips, grade 2 in seven hips, and grade 3 or 4 in fifteen hips. The average center-edge and acetabular angles were 40 degrees (range, 0 degrees to 61 degrees ) and 32 degrees (range, 20 degrees to 43 degrees ), respectively. With the numbers studied, no significant association was detected between outcome and the modifiable risk factors of body mass index or age at the time of surgery. Hips in patients with bilateral involvement were at significantly greater risk of failure (p = 0.02). This method of treatment achieves a 54% rate of survival of the hip at forty-five years. Two-thirds of the surviving hips have an excellent prognosis forty to forty-eight years after the index procedure according to the Kellgren and Lawrence score.