Thirty patients with a mild cubital tunnel syndrome were followed clinically and electrophysiologically for a mean period of 22 months. Ninety percent became asymptomatic. It was possible to delineate electrodiagnostic guidelines indicating which patients were likely to deteriorate. It is suggested that patients with a mild cubital tunnel syndrome in whom follow-up studies show an across-elbow motor conduction velocity of < 41 m per second and/or a motor latency from above the elbow of > 10.2 msec are going to develop a motor deficit. Surgical decompression of the cubital tunnel at this time should result in a more complete recovery of a greater number of patients.