With the increased life expectancy of humans, the physicians are faced to more and more elderly patients. Kidneys change both structurally and functionally with age. Hyalinosis of arterioles and fibrous intimal thickening of the arteries leading to sclerosis, decreased number of nephrons, increased percentage of sclerotic glomeruli, progressive interstitial fibrosis, increased renal vascular resistance, decreased glomerular filtration rate, increased filtration pressure, podocyte damage, decreased concentration ability and hyporeninemic hypoaldosteronism are among these changes. The major clinical reflections of these changes are globally decreased renal function, mild proteinuria, distorted fluid and electrolyte balance with mild polyuria, hyponatremia and hyperkalemia. It is still unclear whether aging alone is responsible for decline in renal function in elderly; or this deterioration is due to comorbidities common in this population. Pathogenesis of aging-related changes in renal function is not fully elucidated; but genetic factors, recurrent attacks of acute kidney injury, aggressive strategies to lower blood pressure, accumulation of advanced glycosylation end products, decreased PPAR-γ expression, increased endothelin-1 expression, reduced nitric oxide generation and accumulation of asymmetric dimethylarginine were reported to have a role in the mechanism. Whatever this mechanism is; it is vital to treat elderly patients with great caution knowing that overtime these possible changes might occur with kidney functions.