Twenty-nine patients with 34 ulnar deficient limbs were studied; the average follow-up was 7.7 years. To permit early determination of prognosis and decisions regarding treatment, four subtypes of this condition have been identified. Progressive ulnar deviation of the wrist was not observed in any case, and the fibrocartilaginous ulnar anlage was resected only to correct fixed deformities of the wrist. The most useful operation was humeral or radial osteotomy to correct the hand on flank deformity. A group of patients who were optimally treated with prosthetic fitting is discussed.