Studies in experimental animals and humans have demonstrated that adaptive compensatory changes in renal growth and function are influenced substantially by the age of the subject at the time that viable renal tissue is removed surgically or destroyed by disease. The compensatory response is enhanced in neonatal subjects, compared to the adult, when normal renal growth is characterized by hyperplasia, while in later life the response is blunted, in association with renal senescence and a decline in both mass and renal function.