BACKGROUND: The nerve conduction study (NCS) is one of the most important diagnostic tools used to evaluate the function of large myelinated nerve fibers. However, the NCS in patients with diabetic polyneuropathy, who have senso-ry and motor abnormalities on neurological examination, are frequently found to be within normal limits. Somatosensory Evoked Potentials (SEP), F-waves, and NCS were performed to determine their usefulness in detecting electrophysiologic abnormalities in the early stages of patients with diabetic polyneuropathy. METHODS: Posterior tibial SEP (PTSEP) studies were performed in thirty patients with clinically suspected diabetic polyneuropathy who had with-in normal values of NCS involving the upper and lower extremities. PTSEP, F-wave, and NCS were also performed in age and height matched eighteen normal participants. RESULTS: The mean latencies of spinal evoked potentials (T12) and cortical evoked potentials (P1) were significantly prolonged in the diabetic patients compared to the control group (p < 0.05). The mean central conduction times and F wave latencies had no significant differences between the patients and control groups (p > 0.05). CONCLUSIONS: We found the SEP study to be a useful diagnostic test for detecting diabetic polyneuropathy.