INTRODUCTION AND OBJECTIVE: Increasing levels of homocysteine (Hcys) are related to decreased nitric oxide synthesis in the vascular endothelium and also to erectile dysfunction (ED). We investigated the traditional risk factors of ED and plasma levels of Hcys in diabetic patients. METHODS: Sixty-two men with type 2 diabetes and ages of between 40 and 70 years were included in the study. Detailed medical and sexual history and physical examination were performed. Erectile function was assessed with the International Index of Erectile Function. All participants were evaluated for fasting and postprandial plasma glucose, HbA1c, total cholesterol, triglyceride, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, apolipoprotein A, apolipoprotein B-100, vitamin B(12), folic acid, and plasma Hcys levels. Patients were evaluated for diabetic neuropathy. Colored penile Doppler ultrasonography was used to detect vascular abnormalities in diabetic patients with ED. RESULTS: Fasting plasma glucose, postprandial plasma glucose, and HbA1c levels were significantly higher in diabetic patients with ED (P<.05). In addition, Hcys levels were slightly high in diabetic patients with ED (P=.079). Logistic regression analysis revealed that high levels of HbA1c (P<.01) and Hcys (P<.05), and smoking status (P<.01) were the main determinants of the presence of ED in our diabetic population. CONCLUSION: We conclude that traditional risk factors, poor metabolic control, and smoking are important in ED generation in diabetic patients. In addition, Hcys, which is an important risk factor in atherogenesis, seems to be important in ED generation in diabetic patients.