The authors performed nerve conduction studies on 54 hands in patients referred with the clinical diagnosis of carpal tunnel syndrome. The authors studied the motor and sensory latencies of the median and ulnar nerves and compared them with each other. The authors divided the results into hands with no, mild, moderate, or severe carpal tunnel syndrome. The authors correlated these results with the presences or absence of the Phalen's sign. The authors concluded that the Phalen's sign is present mostly in the moderate to severe median nerve entrapment, but still can sometimes be present as a false positivity in normal hands.