Ten consecutive patients were treated by one surgeon for an atrophic nonunion of the proximal ulna. There were six men and four women with an average age of 47 years. Nine of the initial injuries were fracture-dislocations (seven posterior Monteggia lesions and two transolecranon fracture-dislocations) and one was a fracture of the proximal ulnar and radial diaphysis. The nonunion was associated with failed operative fixation in nine patients and occurred after treatment in cast in one patient. Three patients had synovial pseudarthroses and eight had bony defects. Debridement of the nonunion, autogenous cancellous bone grafting, and contoured limited-contact plate fixation were done at an average of 36 months after the original injury. The patients were followed up for an average of 39 months. Union was achieved in all 10 patients. The average arc of ulnohumeral motion was 105 degrees and the average arc of forearm rotation was 130 degrees. According to the system of Broberg and Morrey five patients had an excellent result, four had a good result, and one had a fair result. The fair result was attributable to proximal radioulnar synostosis and severe ulnohumeral arthrosis. Atrophic nonunion of fractures of the proximal ulna usually follow a complex injury treated with inadequate fixation. Stable plate fixation and autogenous bone graft predictably lead to union, but the functional result may be limited by associated problems.