We studied the association between erythrocyte aggregation (EA) and erectile dysfunction (ED) in men with coronary artery disease (CAD). Men with CAD documented by coronary angiography filled the Sexual Health Inventory for Males questionnaire to detect ED and assess its severity. EA was evaluated by filming slides of blood smear. Low percentage of slide field covered by erythrocytes represented increased EA. Overall, 133 men with CAD, mean ages 62.4+/-12.2 years, were included: 100 (75.2%) with ED and 33 (24.8%) without ED. EA was increased among men with ED compared with men without ED (percentage of slide field covered by erythrocytes 66.7+/-14.7 vs 73.1+/-14.5%; P=0.03). After adjustment for age, diabetes mellitus, hemoglobin and hematocrit levels, EA was associated with ED severity (r=0.18; P=0.038). We conclude that EA is increased in men with CAD and ED. This finding may be relevant to the pathophysiology of ED in men with CAD.