We determined the association between the severity of erectile dysfunction (ED) and traditional cardiovascular risk factors, including metabolic syndrome (MS). A total of 141 ED patients were divided into three groups on the basis of ED severity, which was determined using the International Index of Erectile Function (IIEF) scores. The prevalence of MS among the ED patients was 32.6%. Significantly lower IIEF scores were noted in patients with MS than in patients without MS (7.6+/-6.4 vs 11.6+/-7.4, P=0.003). As assessed by the anthropometric indices of body mass index, waist circumference and waist-to-hip ratio, obesity was detected in 58.9, 54.6 and 32.6% of the patients, respectively. Of the 141 patients, 39 had mild, 24 had moderate and 78 had severe ED. Statistically significant differences were noted among the different ED severity groups with regard to the presence of hypertension, systolic blood pressure, presence of MS and number of MS components. Multivariate analysis showed that the odds ratio for high-low-density lipoprotein (LDL) cholesterol level in moderate and severe ED, determined with reference to mild ED, were 9.346 and 6.452, respectively. The presence of MS, number of MS components, and certain traditional cardiovascular risk factors, particularly high-LDL cholesterol level and hypertension, may influence the severity of ED.