Previous studies have shown good clinical results following anterior transposition of the ulnar nerve for compression neuropathy. However, no studies have examined all patients pre- and post-operatively with both clinical and electrophysiological studies to determine if a correlation exists. Twenty-three of 24 (96%) anterior transpositions performed consecutively over 6 years were followed up at a mean of 33.2 months with clinical and electrophysiological examinations. All patients were male "blue-collar" workers with a mean age of 52.1 years. The mean duration of preoperative symptoms was 11.3 months. Preoperatively, 30% were graded moderate and 70% severe. The motor conduction velocity (MCV) across the elbow and electromyography (EMG) correlated with the severity of the clinical findings. Postoperatively, 70% of patients improved, with 40% having a good result and 30% fair, and the MCV improved to a highly significant degree (P less than 0.0005). Thirty percent had a poor result with no clinical improvement, yet the MCV improved to a significant degree (P less than 0.05). There was no correlation between the clinical result and the distal motor or sensory latencies, MCV below the elbow, or EMG. Advanced age, duration of preoperative symptoms, diabetes, hypertension, alcoholism, etiology, type of transposition, tourniquet time, and atrophy did not correlate with a poor result, either clinically or electrophysiologically. Severe clinical findings confirmed by electrophysiological studies do not contraindicate surgery and have a reasonable success rate. In conclusion, preoperative electrophysiological studies correlate with the clinical findings but postoperative ones do not, including the MCV. The MCV improves after anterior transposition of the ulnar nerve regardless of the clinical outcome.(ABSTRACT TRUNCATED AT 250 WORDS)