Twenty adults (32 hips) with acetabular dysplasia were followed up for an average of 22 years to determine the natural history of the disorder. Initially, all hips had a center-edge (CE) angle of Wiberg of 20 degrees or less and an essentially intact Shenton's line with no roentgenographic evidence of osteoarthritis. Average patient age initially was 43 years (range, 27-57 years) and at final follow-up examination, 65 years. Various parameters of hip integrity were measured, including the CE angle of Wiberg, acetabular angle of Sharp, percentage of the femoral head covered by the acetabulum, acetabular depth, and inclination of the lateral lip of the acetabulum. None of these indicators proved a reliable prognostic aid for predicting the rate at which the osteoarthritis process supervened in any one case.