A variety of anatomic abnormalities in the aging kidney have been identified, including decreased kidney size, increased glomerular sclerosis, and arteriolar vascular changes. Physiologic changes, including decreased renal blood flow, decreased glomerular filtration rate, altered renal tubular function, and altered renal endocrinologic function, have also been described. The clinical consequence of these changes is an altered ability of the aged kidney to respond to stress, either due to illness or due to therapeutic interventions by physicians. Extra caution and vigilance is therefore needed when caring for the elderly.