An 8-year-old boy with a diagnosis of osteosarcoma of the proximal humerus who was treated by osteoarticular resection and allograft–prosthesis composite reconstruction. A preoperative anteroposterior radiographic view (A) showing a lytic lesion of the proximal humerus. A coronal-T1 (B) magnetic resonance image showing the extent and location of the tumor. Radiographs showing allograft–prosthesis composite reconstruction at the 1-month (C) and 4-year (D) follow-up showing complete consolidation and integration of the allograft at the junction of the host bone and the graft. Allograft–prosthesis composites may be an alternative to modular prosthesis in children with bone sarcoma of the proximal humerus who have a small size of bone.