We compared 63 hips (Catterall Groups 3 and 4) contained by femoral osteotomy with 85 untreated hips and found that 50.7 per cent of treated patients developed congruous spherical femoral heads in contrast to 14.1 per cent of those untreated. We have also considered certain other features relevant to the outcome. We suggest that the indications should not be modified on the grounds of early age of onset. Relief from weight-bearing does not appear to improve the results of containment. We have assessed the shortening which follows femoral osteotomy and conclude that this is only significant when there is growth disturbance at the capital epiphysis. These changes are at least as frequent in untreated patients.