We have retrospectively reviewed the clinical, preoperative ultrasonographic, and operative findings of eight patients who had tardy ulnar nerve palsy caused by a cubitus varus deformity. The mean varus angle on the affected side was 23°. With preoperative ultrasonography, the anterior dislocation of the ulnar nerve from the medial epicondyle was detected in dynamic scanning of short-axis images, and long-axis images revealed nerve compression and kinking in the proximal border of the flexor carpi ulnaris. Operative findings revealed compression of the ulnar nerve by a fibrous band, which was released in all cases. The cause of the tardy ulnar nerve palsy in this series of patients was constriction by a fibrous band and kinking in the proximal border of the flexor carpi ulnaris due to ulnar nerve dislocation from compression resulting from the forward movement of the medial head of the triceps brachii muscle.