A progressive deterioration of renal anatomy and renal function with aging is inevitable. Glomeruli become sclerotic, renal mass declines, kidneys are shrinking and creatinine clearances decreases about 50% after the third decade of life. Renal aging in accelerated by risk factors of arteriosclerosis. The relationship of serum creatinine and creatinine clearance changes with age, since creatinine production is diminished. Old kidneys show a reduced ability to compensate stress, e.g., infection, medication, changes in blood pressure, and the risk of acute renal failure is increased. A glomerulonephritis in advanced age may be caused by a vasculitis; despite rapidly progressive course, early treatment can often improve renal function. The dosage of drugs eliminated by the kidneys has to be adapted in old patients. Despite only moderately elevated serum creatinine, renal function may be severely reduced in old persons and dialysis may be indicated. Dialysis and renal transplantation are possible therapeutic options despite advanced age.