Both erectile dysfunction (ED) and vascular disease share the same risk factors and the two conditions often coexist, with endothelial dysfunction being the common underlying pathophysiology. Up to two-thirds of all patients with clinically evident coronary artery disease (CAD) have ED. Because of their smaller size, the same degree of lipid plaque burden has a greater effect on the penile arteries compared with the coronary arteries. As a result, the clinical consequences of penile vascular disease (ED) frequently manifest 2-3 years before the consequences of coronary atherosclerosis. This phenomenon has led to the widespread view that ED is a silent marker of vascular disease, particularly CAD, in otherwise asymptomatic men. The Second Princeton Consensus Guidelines reflect this by stating that a man with ED and no cardiac symptoms should be considered a cardiac (or vascular) patient until proven otherwise. For most men with no cardiac symptoms, we therefore have 2-3 years from ED onset to reduce the risk of a cardiovascular event. This article discusses the rationale for the link between ED and CAD, with reference to endothelial dysfunction, and the role of ED as an important means of identifying men at risk of vascular disease.