Diabetes is the leading cause of chronic renal failure. However, in the early phase of diabetes, before complications have set in, the glomerular filtration rate (GFR) is elevated in a substantial portion of patients. Kidney size is also increased. These two phenomena result from heightened single-nephron GFR and expanded nephron size, respectively. While the two observations are presumed to be causally linked, it remains to be settled which is cause and which is effect. The clinical importance of these early aberrations derives from two lines of evidence. The first and strongest shows that the hyperfiltration, or more accurately, the heightened glomerular capillary that drives the filtration, damages the glomerulus (1). Second, some data also suggest that enlargement of the kidney, or glomerulus in particular, may contribute to nephropathy by abetting the augmented filtration, by stresses or deficiencies imposed by excess size, or by both (2).