The energy expended during walking by sixteen children who had proximal femoral focal deficiency was measured to compare the outcomes after Syme amputation (seven subjects) with those after Van Nes rotational osteotomy (nine subjects). Multivariate regression analysis revealed that the subjects who had had a Van Nes procedure had a mean oxygen cost (energy per unit of body mass expended per distance walked) that was 0.12 milliliter per kilogram of body mass per meter lower than that of the subjects who had had a Syme amputation (p = 0.001). The subjects who had had a Van Nes procedure tended to walk faster (p = 0.07). A significant decrease in the oxygen cost as a function of increasing age was observed for both groups (p < 0.0001, r2 = 0.79). We believe that the reduced energy expenditure associated with the Van Nes rotational osteotomy is one of several factors to consider when deciding which operation should be done for children who have proximal femoral focal deficiency.