BACKGROUND: Carpal tunnel syndrome (CTS) is the most common mononeuropathy encountered in clinical practice. When performing routine diagnostic nerve conduction studies (NCS) in patients with CTS, we sometimes happen to be confronted with patients who have no definite electrophysiological evidence of CTS. We therefore evaluated the diag-nostic sensitivities of several parameters in NCS for CTS patients. METHODS: We analyzed 187 patients (262 hands) who were diagnosed with CTS clinically and electrophysiologically for the past 4 years in this hospital. RESULTS: Significant abnormal findings of nerve conduction velocity (NCV) were noted in the palm to wrist (P-W) seg-ment( 98.5%), thumb-wrist (I-W) segment (97.3%), distoproximal ratio in the third finger (95.0%), and the terminal latency (71.4%) of the median nerve. There were no statistical differences in the abnormal NCVs between the male and female groups. The sensitivity of each compartment parameters were obtained in the female groups and statistical dif-ferences were found in the sensory NCV of the P-W segment and compound nerve action potential (CNAP) amplitude of the I-W segments in patients between the ages of 40 and 60. The sensory NCV of the P-W segment was especially more significant in this age group. There were statistical differences in the amplitude of the index finger to wrist (F-W) and P-W segments between the denervated electromyography group and normal group (p < 0.05). CONCLUSIONS: In clini-cally suspected CTS, the most sensitive tests were the sensory NCV of the P-W segment, I-W segment, and distoproxi-mal ratio in the third finger. Therefore, the sensory NCV of the P-W segment should be performed first. If the results of this test are unremarkable, then, the next tests should include the sensory NCV of the I-W segment and the distoproxi-mal ratio should be performed before ruling out the diagnosis of CTS.