Most patients who develop Legg-Calve-Perthes disease have unilateral involvement. For those children who do develop bilateral involvement, the disease and its outcome have not been characterized. This study reviewed the records and radiographs of 83 patients (20 girls and 63 boys) with bilateral Legg-Calve-Perthes disease. The patients were then divided into 3 groups based on the Waldenstrom stage at the time of the first radiograph. In Group I (26 patients), both hips were in the same stage. In Group II (45 patients), the hips were in a different stage. In Group III (12 patients), the first hip was well into the remodeling stage by the time the second hip became affected. Twenty of the 83 patients (24%) were girls. There were significantly more lateral pillar group A hips on the second side than the first side in Groups II and III, and only 10 of the 45 patients (22%) in these groups had more severe disease in the second hip. When compared with data from a group of hips with unilateral involvement, there were significantly more hips with a Catterall group I rating in the patients with bilateral involvement. In general, the Stulberg et al. class assigned appeared to be independent of bilaterality. It appears that the development of bilateral disease is an independent event. The data in the present study do not support that onset of disease in one hip leads to disease or causes a more severe disease in the second hip.