Diagnosis of carpal tunnel syndrome (CTS) is usually made on the basis of clinical and electrophysiologic data. Other tests, however, such as ultrasound and CT, have enabled us to acquire additional information regarding the anatomical definition of the structures inside the carpal tunnel. The superior quality of MRIs soft-tissue definition led us to employ it in cases of median nerve compression at the wrist in order to determine its true diagnostic value. We compared the preoperative electrophysiologic and MRI findings in 23 cases of CTS which had undergone surgical decompression of the median nerve at the wrist. Exact correspondence with the intraoperative findings confirmed the reliability of the anatomical information provided by MRI, yet the same comparison revealed that correct "functional" information could be provided only by the electrophysiologic tests.