OBJECTIVE: The aim of this study is twofold. First, to assess the relationships between the cross-sectional area (CSA) of the median nerve (MN) calculated at ultrasound (US) and: (1) patient's perception of his/her symptoms and hand function; (2) clinical severity of CTS; (3) neurophysiological classification; (4) hand distribution of symptoms. Second, to assess the sensitivity of ultrasonography (US) and neurophysiology in the diagnosis of CTS using clinical measures as gold standard. METHODS: We performed a prospective study by using multidimensional assessment: clinical (Historic and Objective scale, Hi-Ob), neurophysiological, patient-oriented measures (Boston Carpal Tunnel Questionnaire, BCTQ) and high-resolution US. The dominant hands of 54 consecutive patients who were referred to our neurophysiologic laboratory with clinical signs of CTS (43 females, mean age 53.3, range 30-80, SD: 13.1) were examined. RESULTS: A statistically significant correlation was found between the CSA of the MN at wrist and (1) hand function (according to BCTQ, r=0.35, p=0.01), (2) clinical scale (Hi-Ob scale, r=0.51, p