A variety of age-related anatomic and functional alterations in the kidney have been described. Anatomic abnormalities in the aging kidney include a decrease in kidney size, increased glomerular sclerosis, altered tubular structure, and an altered pattern of vascular flow. These anatomic abnormalities are associated with renal functional abnormalities, including decreased renal blood flow, and glomerular filtration rate. Altered renal tubular function, including impaired handling of water, sodium, acid, and glucose, may also be present. Impaired "endocrinologic" functioning manifested by changes in the renin-angiotensin system, vitamin D metabolism, and antidiuretic hormone responsiveness have been reported. The kidney is constantly exposed to the effects of a variety of potentially toxic processes. These range from environmental toxins and drugs, to a variety of chronic medical illnesses including hypertension, diabetes, and atherosclerotic disease. In this context, differentiation of "aging" effects from nephrotoxic effects resulting from these other processes is difficult. It has been argued that hypertension is an important factor in the development and progression of renal insufficiency in the elderly. The relationship between hypertension, glomerular hyperfiltration, atherosclerosis, and progressive renal dysfunction needs further study. Further research may allow the rational recommendation of interventions designed to control age-associated changes in renal function.