From 1992 to 1994, 29 middle and 19 distal humeral shaft fractures (39 acute fractures, six nonunions, and three pathologic fractures) in 48 patients were treated by retrograde locked nailing. The first eight acute fractures were treated with Seidel nails, the other 40 fractures with specially designed humeral locked nails. Nails were inserted from the supracondylar (6) or the olecranon fossa (42) entry portal. With a single operation, all acute fractures and nonunions achieved osseous union without serious complications. The average time to union was 8.2 weeks for acute fractures and 14.2 weeks for nonunions. Recovery of shoulder function was complete. Elbow motion was excellent in all but one nonunion that resulted from a Type IIIB open fracture. Two patients with supracondylar entry had apex to posterior angular malunion. One patient with a distal comminuted fracture had varus malunion. Three patients had an iatrogenic bony split, but healing was unaffected. Patients with pathologic fractures maintained satisfactory arm function postoperatively. Given the few complications and good functional recovery seen in this study, retrograde locked nailing appears to be a good alternative treatment in middle and distal humeral shaft fractures. The olecranon fossa approach, with more linearity to the humerus, is preferred. In the authors' experience, humeral locked nails are inserted more easily and are associated with fewer complications than are Seidel nails.