Purpose: We investigated the relationship between oxidative stress and diabetic erectile dysfunction. Materials and Methods: A total of 23 patients with a mean SD age of 56.7 +/- 5.6 years, a history of type 2 diabetes for 10.0 +/- 8.3 years and erectile dysfunction, as tested by the International Index of Erectile Function questionnaire, but without vascular and neurological complications, and 15 age matched patients with diabetes without erectile dysfunction were recruited. Circulating monocyte oxidative activity by cytofluorometry, and endothelin-1, intercellular adhesion molecule-1, plasminogen activator inhibitor-1 by enzyme linked immunosorbent assay were evaluated in all patients in the study. Results: Monocyte free radical production, and total and low density lipoprotein cholesterol were higher in patients with than in those without erectile dysfunction (p