Congenital pseudarthrosis of the ulna is an extremely rare disease that is usually associated with neurofibromatosis. Various treatments have been introduced such as conservative treatment, nonvascularized bone graft, free vascularized fibular graft, one bone forearm procedure and the Ilizarov technique. However, it is difficult to obtain bone union. We report a case of pseudarthrosis of the distal ulna that was treated by a one bone forearm procedure.