Erectile dysfunction (ED) and coronary artery disease (CAD) overlap in risk factors, aetiology and clinical outcomes. It has become clear that ED is an important marker of vascular disease throughout the arterial tree – including CAD, stroke and diabetes. Epidemiological studies have demonstrated a close association between ED and vascular disease. The shared aetiological factor is endothelial dysfunction. The fact that ED tends to precede the onset of symptoms of other vascular diseases – because blood vessels in the penis are narrower in diameter than elsewhere in the body so blood flow is restricted sooner by atherosclerosis – means that it can be used as a ‘window’ on vascular health. There is growing evidence that patients presenting with ED should be investigated for cardiovascular disease (CVD), including diabetes, even if they have no symptoms. Early detection could facilitate prompt intervention and a reduction in long-term complications. Treatments that reduce endothelial dysfunction offer the potential of improving the functioning of the entire vascular system, improving outcomes in CVD and diabetes, as well as providing effective treatment for ED.