A 16-year-old boy presented with a painful deformity of the forearm. At the age of 11 years, he had sustained a Monteggia fracture-dislocation. Radiographs indicated nonunion of the ulna, radial head dislocation, and degenerative changes of the radiocapitellar joint. The longstanding nonunion of the ulna had caused very severe growth disturbance. Despite severe deformity, the patient had had relatively good motion. To regain forearm stability with maintaining motion, we corrected the deformity and stabilized the ulna with a vascularized fibular graft. Two years after surgery, the patient had a good range of motion without pain and grip strength was increased.