Current information on the nature, pathogenesis and treatment of diabetic glomerulosclerosis is reviewed. The fundamental lesion is one of the glomerular basement membrane, a complex layer of collage-like and other peptides; thickening of this membrane, seen microscopically, is due to the presence of an increased amount of membrane material of normal composition. There is little reliable evidence relating the frequency of glomerulosclerosis to the quality of control of the diabetic state, but indirect evidence from patients with secondary diabetes and from a variety of studies in animals indicates strongly that the glomerular lesion is a consequence of the abnormal metabolic state and can be prevented by adequate treatment of the diabetes. A concept of the pathogenesis of the glomerular lesions and renal failure is presented, but there remain large gaps in knowledge of the mechanisms involved. Treatment of chronic renal failure by maintenance renal dialysis and renal transplantation is not as successful in persons with diabetes as in those without this condition; however, the results appear to be improving, and transplantation particularly holds much promise.