We reviewed the records and roentgenograms of all patients with Legg-Calvé-Perthes disease who had been seen at our institution between 1940 and 1996. One hundred and five girls (122 hips) and 470 boys (531 hips) were identified. Thus, 18 per cent of the 575 patients in the present series were girls. Seventeen (16 per cent) of the girls and sixty-one (13 per cent) of the boys had bilateral involvement. Although more girls than boys had severe involvement of the femoral head and the lateral pillar, we could not detect a significant difference between the two groups with respect to the distribution of the involvement of the hips according to the system of Catterall or the lateral pillar classification (p > 0.05, beta = 0.99). Serial roentgenograms that showed all four stages of the disease according to the system of Waldenström were available for fifty-two hips in girls and 184 hips in boys. A review of these roentgenograms revealed that the average ages of the girls at the stages of necrosis, fragmentation, reossification, and remodeling were 6.8, 7.3, 7.9, and 9.5 years, respectively, whereas the average ages of the boys were 6.8, 7.3, 7.9, and 9.9 years, respectively. Girls, however, had closure of the affected proximal femoral physis at an average age of 12.9 years, whereas boys had closure at an average age of 15.8 years. Therefore, girls had a shorter potential period for remodeling of the femoral head (average, 3.4 years) compared with boys (average, 5.9 years). Sixty-four girls (seventy-eight hips) and 363 boys (416 hips) had reached skeletal maturity by the time of the latest follow-up and were evaluated according to the system of Stulberg et al.; we could not detect a significant difference between boys and girls with respect to the distribution of the hips according to this system (p > 0.05, beta = 0.99). Although the numbers were too small for statistical analysis, our findings suggest that boys and girls who have the same Catterall or lateral pillar classification at the time of the initial evaluation can be expected to have similar outcomes according to the classification system of Stulberg et al.