Erectile dysfunction (ED) is a common problem in the United States, with estimates that 30 million men suffer with some degree of ED. Although causes include psychogenic, organic, and mixed forms, in middle-aged and older men one of the most common causes is vascular disease. Endothelial dysfunction, even without definitive arterial stenosis, as well as atherosclerosis with definitive stenosis of blood vessels, contributes to the problem. Endothelial dysfunction and atherosclerosis of blood vessels that supply the penis are associated with the same cardiovascular risk factors that affect the coronary arteries: smoking, lipid abnormalities, hypertension, and diabetes.