1. The occurrence of bilateral double-layer patellae in association with multiple epiphysial dysplasia is described in three siblings.

2. Twelve cases of bilateral double-layer patellae have been reported previously, and in all there was an accompanying skeletal dystrophy which, although not diagnosed as such, is likely to have been multiple epiphysial dysplasia.

3. It is suggested that although they occur only in a minority of cases, double-layer patellae when present are a feature of considerable diagnostic value in multiple epiphysial dysplasia. Lateral radiography of the knees may therefore be of assistance in the diagnosis of multiple epiphysial dysplasia.