The management of adolescent radius and ulna diaphyseal fractures is controversial. The purpose of this study was to address the residual deformity and functional outcome following closed treatment of these fractures. Twenty-five older children and adolescents (mean age 13.3 years, range 8.8-15.5) with displaced diaphyseal both-bone forearm fractures underwent closed treatment and were followed for a mean of 49.6 weeks. All fractures united. On the final AP radiograph, the mean angulation was 9 degrees (range 0-18 degrees) for the radius and 8 degrees (0-20 degrees) for the ulna. All patients achieved full elbow and wrist range of motion. Loss of forearm supination and pronation averaged 4 degrees (range 0 to 20 degrees) and 6.8 degrees (0 to 40 degrees), respectively. Closed reduction and casting of displaced both-bone diaphyseal forearm fractures, despite the residual angulation, results in satisfactory functional outcome and should remain a viable treatment option in the management of this injury.