Twenty-six children with fractures of the femur were entered into a prospective study to determine the efficacy of treating certain of these fractures by early spica cast immobilization. They were compared with 50 consecutive patients with similar fractures who were treated prior to the study to determine the potential cost savings and decrease in patient days in hospital. The clinical results of treatment were compared with results from the literature and the previous group where applicable. Our conclusion from this study is that most femoral shaft fractures in children under 10 years of age can be treated by closed reduction and early spica cast immobilization with results that are at least as good as those achieved by conventional methods, and with a 70% savings in hospital cost. Factors such as obesity, swelling, shortening, comminution, and fracture type can all combine to give relative contraindications for the use of this technique.