In the past the opinion prevailed that renal prognosis was less adverse in non-insulin-dependent diabetes mellitus (NIDDM) as compared with insulin-dependent diabetes mellitus (IDDM). This notion has to be revised in the light of recent evidence, based on epidemiologic data of NIDDM patients reaching endstage renal failure and a comparison of the cumulative prevalence of proteinuria and renal failure, respectively, in NIDDM as compared with IDDM. It has also been established that initial renal hemodynamic changes are quite comparable in NIDDM and in IDDM. It follows that past complacency about the renal sequelae of NIDDM is no longer justified and that preventive measures to interfere with the development of diabetic nephropathy are similarly important in NIDDM and IDDM.