Purpose: Genu valgum in Legg-Calve-Perthes disease (LCPD) is not a known complication. We investigated whether this valgus tendency is a complication of femoral varus osteotomy (FVO) or the sequela of the disease process itself, and what are the related factors. Materials and Methods: 35 patients treated by FVO and 38 by abduction orthosis (AO) were selected for this study. Only those patients with unilateral involvement, fragmentation stage, Catterall Group III or IV, and who were followed-up to full skeletal maturity were included in the study. We measured mechanical axis deviation percentage and hip-knee-ankle angle for femorotibial alignment, and mechanical lateral distal femoral angle and medial proximal tibial angle (mMPTA) for knee orientation on teleoroentgenograms and compared the affected and normal limbs. Results: All measurements, excluding the mMPTA, demonstrated a tendency of relative genu valgum versus the opposite normal limbs. This tendency was observed in both groups. There was no statistically significant difference between the two groups. Conclusion: Genu valgum occurred in 66% to 70% of the LCPD patients. Four factors were found to be significantly correlated with valgus shift: increased medial bowing of the femoral neck, decreased acetabulum head index, coxa magna, and limb shortening. Multivariate regression analysis identified limb shortening as the factor most responsible for valgus shift.