People with high blood pressure (BP) are more likely to develop heart, blood vessel, and kidney disease. Drugs that lower BP may prevent these complications. Drugs known as angiotensin-converting enzyme (ACE) inhibitors are thought to be best for preventing kidney failure in people with high BP and lower kidney function. Diuretics, also called water pills, are thought to be best for preventing cardiovascular disease (CVD) in people with high BP regardless of level of kidney function. How these and other BP drugs compare in their ability to prevent CVD and kidney failure has never been directly studied.