Background/aim: The aim of this study was to assess the diagnostic utility of the ultrasonographic ratio of median nerve cross-sectional area (m-CSA) to ulnar nerve cross-sectional area (u-CSA), the m-CSA/u-CSA ratio, in carpal tunnel syndrome (CTS). Materials and methods: Fifty patients with positive symptoms and electromyography results of CTS and 50 healthy matched control subjects were evaluated. Ultrasonographic m-CSA and u-CSA measurements of each participant were made at the level of the pisiform bone and the m-CSA/u-CSA ratio was calculated. Results: Using the m-CSA cut-off value of 11.95 mm2 showed a sensitivity of 80% and a specificity of 80% while using a cut-off value 2.95 for the ratio of m-CSA/u-CSA showed a sensitivity of 86% and a specificity of 72% in the diagnosis of CTS. Conclusion: The ratio of m-CSA/u-CSA at the level of the pisiform bone was not detected to be superior to m-CSA in the diagnosis of CTS.