Objectives: Six cases of tardy ulnar neuropathy caused by cubitus varus deformity are presented. Clinical features and electrodiagnostic study of six cases were analysed to understand the mechanim of nerve palsy and the usefulness of electrodiagnostic study.

Methods
Electrodiagnostic study and elbow flexion test were performed and elbow varus angle, internal rotation angle of shoulder, biceps and brachioradialis muscle activities were measured in 6 patients

Results
Decreased ulnar nerve motor conduction velocities in the elbow segment was shown in 5 patients. Prolonged distal latency and reduced amplitude of ulnar sensory nerve action potentials were shown in one patient. Needle electromyography showed large amplitude motor unit action potentials in ulnar innervated forearm or hand muscles. The mean values of varus angle and internal rotation angle of humerus were 21^o, and 28^o, respectively. Brachioradialis showed relatively higher activity than biceps brachii in the early phase of elbow flexion. Three patients underwent surgery and showed immediate symptom relief.

Conslusion: Tardy ulnar nerve palsy in cubitus varus thought to be caused by internal rotation of distal segment of humerus, stretching of ulnar nerve, snapping of the medial head of triceps on ulnar nerve and anterior transposition and compression of ulnar nerve. The three dimensional corrective osteotomy could be the most efficient treatment to restore the anatomic alignment of the elbow joint.