Aldosterone modulates cardiovascular and renal injury and fibrosis in animal models. This review explores the hypothesis that aldosterone causes injury and fibrosis, in part, through effects on plasminogen activator inhibitor-1, the major physiological inhibitor of plasminogen activators in vivo. Aldosterone interacts with angiotensin II to increase plasminogen activator inhibitor-1 expression in vitro and in vivo. Plasminogen activator inhibitor-1, by inhibiting the production of plasmin from plasminogen, tips the balance in favor of extracellular matrix accumulation and promotes fibrosis. Aldosterone receptor antagonism decreases both PAI-1 expression and fibrosis in animal models. These findings have implications for the clinical management of cardiovascular and renal disease.