1. A study of fifty-nine patients with protrusion of the acetabulum showed that they fell into three age groups: those in their teens, those aged thirty-five to fifty years, and those presenting from fifty-one years onwards.

2. The juvenile age group was investigated clinically and biochemically but no causative metabolic factor was found.

3. The familial incidence was confirmed by radiological and biochemical surveys of several families.

4. The results of treatment show that when conservative treatment is insufficient a total hip replacement gives the best result from operation.