A prospective study was carried out to investigate any correlation between electrophysiological and sonographic findings in patients with a clinical diagnosis of carpal tunnel syndrome. A total of 113 patients (113 wrists) in 90 women and 23 men, with a mean age of 60 years, underwent sonographic and electrophysiological examination. Fifty-five patients (48%) had mild, 43 (38%) moderate and 12 (11%) had severe conduction disturbances and three patients had normal conduction. Sonographic measurements showed a cross-sectional area of the median nerve of 9.9 mm² at the forearm and 17.8 mm² at the tunnel inlet. The mean anteroposterior diameter (height) of the nerve at the tunnel inlet was 2.7 mm, and the lowest height inside the tunnel was 1.8 mm. No correlation was found between sonographic and electrophysiological parameters.