OBJECTIVE A low ratio of serum eicosapentaenoic acid to arachidonic acid (EPA/AA) has been associated with coronary artery disease. We retrospectively examined serum concentrations of polyunsaturated fatty acids in patients with arteriosclerosis obliterans (ASO) and in non-atherosclerotic patients. METHODS From April 2011 to March 2012, serum EPA/AA was retrospectively examined in 33 consecutive outpatients with ASO complicated by intermittent claudication and 21 outpatients with hypercholesterolemia without ASO as controls. The Student's t-test was used for continuous variables and Chi-square test for categorical variables, with analysis of covariance adjusting for age, sex, body mass index, smoking, alcohol, and diabetes. RESULTS The ASO group were significantly different with regard to mean age (71.5 vs. 63.9 year-old, p = 0.03), body mass index (21.3 vs. 24.1 kg/m(2), p = 0.002) and morbidity of diabetes mellitus (51.5 vs. 4.8%, p = 0.0004). Serum EPA/AA was significantly decreased in ASO (0.36 vs. 0.61, p = 0.03), when adjusted for age, sex, body mass index, smoking status and alcohol drinking, but was not statistically significant when adjusted for diabetes. CONCLUSIONS Patients with ASO were more likely to have a low EPA/AA ratio and non- diabetic patients with ASO had a significantly reduced EPA/AA.