In animals with reduced renal mass increased glomerular filtration is associated with accelerated glomerular sclerosis. Whether hyperfiltration causes glomerular damage in humans is unknown. Since increased glomerular filtration occurs in obesity, the amount of glomerular sclerosis found in renal autopsy tissue from 46 patients with massive obesity was compared to that found in 46 normal body weight controls. Despite increased kidney weight and glomerular size, obese patients had the same proportion of completely sclerosed glomeruli as controls. In addition, no focal segmental glomerular sclerosis was seen in the obese group. It is concluded that patients with massive obesity have increased kidney weight and nephron size consistent with hyperfiltration. Nevertheless, massively obese patients do not appear to have increased glomerular sclerosis.