The biologic price of aging includes progressive deterioration of renal function and structure. Changes in renal function during normal aging are among the most dramatic of any organ system, so that the glomerular filtration rate of healthy octagenarians is only one-half to two-thirds that measured in young adults.'T2 When acquired renal disease is superimposed on the kidney already compromised by age-related structural and functional changes, progression to end-stage renal disease may be hastened appreciably. In this article, we consider the functional and structural changes that occur in the aging kidneyJ3 and the factors which may modify the course of age-and diseaserelated progressive renal insufficiency.