Ulnar lengthening, one of the operative treatment methods for Kienbock's disease, is based on the theory that ulnar minus variance is a significant causative factor of Kienbock's disease. It is considered that this method can promote the revascularization of the devascularizied lunate by reducing the forces concentrated at the wrist joint and that over-all carpal collapse is halted or reversed when the ulnar part of the carpus is supported better. 4 patients with Kienbock's disease treated by ulnar lengthening with iliac bone graft were reviewed after follow-up ranging from12 months to 30months. In all of 4 patients, relief of pain was satisfactory and there was no remarkable complication.