OBJECTIVE: The purpose of this study was to assess the diagnostic utility of the wrist ultrasonography (USG) in patients with and without carpal tunnel syndrome (CTS). METHODS: Individuals with electrodiagnostically proven CTS patients and healthy control subjects were enrolled prospectively. USG was done 60 wrists of 48 patients with CTS and 36 wrists of 18 controls. The USG analysis included median nerve cross sectional area (CSA) at the level of carpal tunnel inlet. We also evaluated the relationship between median nerve CSA at the level of carpal tunnel inlet and severity grade of nerve conduction test in CTS patients. RESULTS: The median nerve CSA at the level of carpal tunnel inlet was significantly larger in CTS patients (13.6 mm2 versus 7.7 mm2, p<0.0001). And there was an association between median nerve CSA and severity grade of nerve conduction studies (p=0.036). Receiver operating characteristics (ROC) analysis yielded sensitivity of 86.7% and specificity of 88.9% using a cut-off value of 9 mm2. But the specificity was increased to 97.2%, although sensitivity was decreased to 78.3%, when using cut-off value at 10.1 mm2. CONCLUSION: Ultrasonographic measurement of the median nerve CSA at carpal tunnel inlet was useful in diagnosis of CTS. According to ROC analysis, USG is used as a complementary test for electrodiagnostic test.