Copeptin is a marker of endogenous vasopressin secretion. Population-based data of the PREVEND Study show that men and women with high plasma copeptin have a highly prevalent microalbuminuria in addition to the low level of hydration typical of persons with high vasopressin secretion. The association of plasma copeptin with microalbuminuria suggests that vasopressin might have a role in kidney dysfunction via effects on the permselectivity of the glomerulus and/or on tubular albumin reabsorption.