Background Carpal tunnel syndrome (CTS) is the most common entrapment neuropathy caused by compression of themedian nerve beneath the transverse carpal ligament. CTS can be correctly diagnosed by the patients' description of symptomsand electrophysiological tests that measure nerve conduction through the wrist. Many previous studies reported variousrisk factors of CTS, such as obesity, diabetes mellitus, thyroid disease and trauma. Obesity is associated with both hyperlipidemiaand CTS. This study focused on the relationship between severity of CTS and serum lipid level. Methods: Onehundred fourteen patients with CTS and 74 controls were divided into four groups according to the severity; normal, mild,moderate and severe. And then serum total cholesterol (TC), triglyceride (TG), low-density lipoprotein (LDL-C) andhigh-density lipoprotein (HDL-C) were measured in each group. Results: There was a positive correlation between TG andCTS severity (p<0.001). But TC, LDL-C and HDL-C were not correlated with CTS severity. Conclusions: These results suggestthat high serum TG may act as an aggravating factor of CTS.