Prospective analysis of 27 medial epicondylectomies in 22 patients with McGowan grade I ulnar neuropathy demonstrated an improvement in clinical symptoms. In all patients a N.C.V. study, in which compression of the ulnar nerve at the cubital tunnel was evident, has been a prerequisite for operation. Conduction velocity across the cubital tunnel averaged 48% of normal (26.4 +/- 8.7 metres per second) preoperatively and increased to 85% of normal (46.7 +/- 9.7 metres per second) postoperatively. A preoperative N.C.V. study allows the achievement of a high success rate, especially in the less well clinically defined group of patients with grade I neuropathy (subjective complaints without any objective signs of muscle atrophy). Medial epicondylectomy is safe and predictable in the treatment of cubital tunnel syndrome.