Aldosterone, the final product of the renin-angiotensin-aldosterone system, is classically viewed as a regulator of renal sodium and potassium handling, blood volume, and blood pressure. Recent studies suggest that aldosterone can cause microvascular damage, vascular inflammation, oxidative stress and endothelial dysfunction. In animal models, aldosterone-mediated vascular injury in the brain, heart, and kidneys leads to stroke, myocardial injury, and proteinuria. These effects may be modified by dietary salt intake; aldosterone-mediated vascular damage is increased in susceptible animals fed a high-salt diet compared to a low-salt diet despite lower plasma aldosterone levels on the high-salt diet. In humans, there is a growing literature supporting the adverse effects of aldosterone in heart failure, hypertension, left ventricular hypertrophy, and renal disease. Aldosterone receptor antagonists are beneficial even in patients on angiotensin converting enzyme inhibitors and attenuate aldosterone-mediated vascular injury by mechanisms that appear to be independent of changes in systolic blood pressure. This review focuses on the adverse effects of aldosterone on the vascular system and describes our current understanding of the underlying mechanisms for this injury.