A controlled, double-blind trial, carried out by Lewis and al., has shown that in 409 patients presenting with insulin-dependent diabetes, proteinuria in excess of 500 mg/day and plasma creatinine of less than 221 mumol/l, captopril treatment was able to reduce the risk of combined events (mortality, renal dialysis and transplantation) by 50% (p = 0.006) and that of doubling plasma creatinine by 48% (p = 0.007). We evaluated the cost/benefit ratio of this treatment on the basis of the medical outcome of this study and economic data for the French health-care system. The cost of the treatment by captopril is totally offset by the reduction in costs obtained by postponing dialysis and kidney transplantation, concomitant antihypertensive treatment and hospitalisation. In this study, the health expenditure savings in the captopril group amounted to 6 million French Francs. Spending 100.-Francs on captopril to treat diabetic nephropathy yielded savings of 575.-Francs. This economic advantage, plus a reduction of 6 in the number of deaths, corresponding to 131 life-years saved, demonstrates the favorable cost-benefit ratio of this treatment strategy.