Twenty of 59 hands (34%) of patients with carpal tunnel syndrome had abnormalities in sensibility testing of both median and ulnar nerves by either two-point discrimination, Semmes-Weinstein monofilament testing, or both. Before surgery, 53% of patients complained of paresthesias and/or numbness in u1nar nerve distribution. Eighty percent of the hands had abnormal Semmes-Weinstein monofilament testing of the ulnar nerve. Thirty-five percent had abnormal two-point discrimination. Forty-one percent had abnormal electromyographic testing of the ulnar nerve. All hands had median nerve decompression alone. Guyon's canal was not released. After surgery, 89% of patients had improvement in paresthesias and/or numbness of the ulnar nerve. Ninety-four percent had improvement in Semmes-Weinstein monofilament testing. Eighty-six percent had improvement in two-point discrimination. Patients with a residual abnormality in ulnar nerve sensibility also had continued abnormality in median nerve sensibility. A significant percentage of patients with carpal tunnel syndrome also have signs and symptoms of ulnar nerve compression. Most improved with carpal tunnel release alone.