Background: Conventional methods in the diagnosis of carpal tunnel syndrome (CTS) in patients with polyneuropathy (PNP) are insufficient. Aims: We suggest that the comparison of the conduction of the median nerve with that of the neighboring peripheral nerves may be more beneficial in the diagnosis of entrapment neuropathy. Setting and Design: The median nerve sensory conduction in healthy volunteers, in cases of CTS, PNP cases without CTS and in cases of PNP in whom clinical findings point to CTS, were compared by palmar cutaneous nerve (PCN) sensory conduction. Materials and Methods: Comparative parameters were difference of PCN-1(st) digits' nerve conduction velocities (NCV), PCN/1(st) digit NCVs ratio, difference of 5(th)-2(nd) digits' NCVs and 5(th)/2(nd) digits' NCVs ratio. Statistical Analysis: The statistical analysis was performed by the SPSS package for statistics. Student t test and receiver operating characteristic were used. Results: Although the ratio of PCN-1(st) digit did not differ significantly between the control group and the polyneuropathy group, there was a significant difference between CTS and PNP+CTS groups and the control group (P < 0.001 and P < 0.001, respectively). The ratio of PCN-1(st) digit nerve conduction velocity was also significantly different between polyneuropathy and PNP+CTS groups (P < 0.001). Conclusion: To diagnose CTS on a background of polyneuropathy in mild cases in which sensory conduction is preserved, the ratio of sensory nerve conduction velocities of the palmar cutaneous nerve and the median nerve 1(st) digit-wrist segment may be a criterion.