Eighty-eight upper extremities of 65 patients with ulnar ray deficiency were reviewed with regard to clinical manifestations. Based on the findings, a subclassification into four types was established: type I, hypoplasia or partial defect of the ulna; type II, total defect of the ulna; type III, total or partial defect of the ulna with humeroradial synostosis; and type IV, ulnar defect with congenital amputation at the wrist. Various manifestations of deficiency were evident not only within the ulnar ray but also in other rays. Hypoplasia of the shoulder and/or proximal part of the humerus was present in some cases of types III and IV. Elbow involvement varied from functioning (type I) to acute flexion contracture (type II) to fusion (type III). In 57 hands the digits and carpal bones in the radial ray showed hypoplasia and/or defect. Central digits and carpal bones were also influenced by ulnar ray deficiency, presenting carpal bone fusion, syndactyly, and delta phalanx.