Seven patients with tardy ulnar nerve palsy from a posttraumatic cubitus varus deformity were reviewed retrospectively. The severity of symptoms was grade I in 3 patients and grade II in 4 patients according to McGowan's classification. The mean internal rotation angle was 30.7 degrees (range, 25 degrees -45 degrees ). The most prominent feature was dislocation of the nerve anterior to the medial epicondyle and entrapment of the nerve by the fibrous band of the flexor carpi ulnaris muscle. Of these 7 patients, 4 were treated by 3-dimensional osteotomy with ulnar nerve transposition, and 3 were treated by anterior transposition of the ulnar nerve. All patients improved clinically, and there was no significant difference between anterior transposition of the nerve in the group with osteotomy and the group without osteotomy. Ulnar nerve instability due to internal rotation deformity and distal entrapment was considered to be the main cause of neuropathy.