Nonunion following diaphyseal forearm fracture is an uncommon complication in children. Compression plate fixation with bone grafting has been the standard method to treat this complication. We report a case of hypertrophic nonunion of the ulna in a child who was treated surgically using an elastic stable intramedullary nail (ESIN) without bone grafting. The nonunion healed 4 months after surgery.