There is now increasing evidence that essential hypertension is a serious risk factor for renal insufficiency. It has been known for many years that malignant essential hypertension rapidly causes deterioration of kidney function. This can be prevented by treatment with anti-hypertensive drugs. Mild-to-moderate essential hypertension causes significant renal function impairment only after a number of years. There are now data suggesting that the decline of renal function caused by mild-to-moderate essential hypertension can be prevented by anti-hypertensive treatment. In recent years, it has been demonstrated that anti-hypertensive drugs have a beneficial effect on the progression of renal insufficiency in patients with diabetic nephropathy and in chronic glomerulonephritis. In these situations, ACE inhibitors appear to be superior to other classes of anti-hypertensive drugs.