Femoral varus osteotomy is one of the most common treatments for patients with symptomatic Legg-Calvé-Perthes disease with more severe deformities. We hypothesized knee valgus alignment at maturity in patients with Legg-Calvé-Perthes disease is an effect of the disease and not an effect of femoral varus osteotomy. We retrospectively compared matched groups of 28 patients with and without femoral varus osteotomy. The two groups were similar with respect to age at onset and classification of Herring et al. The distribution of valgus alignment among patients who had surgery and patients who did not have surgery was assessed at maturity and was similar between the operative and nonoperative groups. The data suggest valgus malalignment (genu valgum) is not a side effect of femoral varus osteotomy in patients with Legg-Calvé-Perthes disease, but rather an effect of the disease. METHODS Level III, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.