Eighteen hips in 15 children showed persistent roentgenographic evidence of congenital acetabular residual dysplasia at four- to eight-year follow-up evaluations. The mean follow-up period was 5.8 years. These hips were subsequently evaluated by magnetic resonance (MR) imaging. MR imaging studies revealed thick unossified chondroepiphyseal cartilage of the acetabular roof adjoining the ilium in all hips. The cartilage in these hips counterbalanced the steep acetabular slope seen on roentgenograms. Initially these hips were regarded as candidates for an acetabular reconstruction, but 11 hips displayed sufficient cartilaginous acetabular coverage on MR images. MR imaging promotes more accurate selection of patients for acetabular reconstruction and aids in the choice of the most appropriate type of acetabular reconstruction.