In adult diabetic patients microalbuminuria is a marker of early vascular damage in the micro- and macrocirculation. Microalbuminuria is a powerful predictor of renal and cardiovascular disease outcome and is associated with other, potentially modifiable, risk factors of vascular damage. Studies of secondary prevention have shown that blood pressure lowering drugs effectively reduce albumin excretion rate. Angiotensin converting enzyme (ACE) inhibitors seem particularly effective in reducing the risk of progression to clinical albuminuria in both insulin dependent and non-insulin dependent diabetic patients and this beneficial effect appears to be long-lasting. Whether this postpones the onset of end-stage renal failure and/or reduces early mortality in these patients remains to be established. Recent studies of primary prevention in insulin-dependent diabetic patients predominantly with normoalbuminuria demonstrate that ACE inhibition reduces significantly the rate of progression of albumin excretion rate and, of great interest, seems to affect beneficially the progression of retinopathy. These results compare favorably with the beneficial effect of intensified insulin therapy and strict blood glucose control in this same group of patients. Thus, ACE inhibitors are a powerful tool to prevent progression of microalbuminuria in diabetes and may prove useful as an adjunct therapy to intensified insulin therapy in the prevention of development of microalbuminuria and of retinopathy progression in insulin dependent diabetes.