Roughly 40% of all patients with insulin-dependent diabetes mellitus (IDDM) develop diabetic nephropathy with proteinuria, hypertension and a decrease in glomerular filtration rate 10 to 20 years after the onset of the disease, and 5 years later most patients suffer from end-stage renal disease. Microalbuminuria, defined as an urinary albumin excretion rate (UAER) between 30 and 300 mg/day, strongly predicts the development of nephropathy in IDDM. Nearly all patients with IDDM, a decreasing glomerular filtration rate and a UAER > 300 mg/day have coexisting hypertensive disease additionally worsening renal function. We review the results of recent long-term studies of the current therapeutic management in diabetic patients by means of better blood pressure control, low-protein diet and near-normal blood glucose control in the early microalbuminuric phase as well as in the later phases of the disease characterized by diabetic nephropathy with a UAER > 300 mg/day. Since the large majority of studies have been performed on IDDM, our conclusions with regard to therapy are only valid in this subgroup of diabetic patients.