The pathogenesis of terminal renal failure is discussed. The following are distinguished: 1. Renal failure occurring against a background of decompensated benign nephrosclerosis, primary and secondary malignant nephrosclerosis, and stenosis of the renal artery. 2. Renal failure caused by loss of glomeruli. It is pointed out that in most glomerulopathies, including diabetic glomerulopathy and renal amyloidosis, terminal renal failure only develops when accompanying disease of the postglomerular vessels leading to interstitial fibrosis impairs the outflow of blood from the glomerulus to such an extent that no more urine is produced. 3. Renal failure in disease of the tubules themselves. It is emphasized that acute renal failure only becomes chronic when interstitial fibrosis develops from the interstitial edema occurring in the early stage of the disease. 4. Renal failure occurring in primary diseases of the renal cortical interstitium. The chronic sclerosing renal diseases arising from acute interstitial nephritis are dealt with, as also are reflux nephropathy, incomplete obstructive nephropathy, analgesic nephropathy, and chronic interstitial rejection reactions in transplanted kidneys.