OBJECTIVE To determine the extent that mortality in IDDM and NIDDM patients is inexcess of that of the general population and examine its relation to hypertension and proteinuriain diabetic patients. RESEARCH DESIGN AND METHODS A stratified random sample of 4,714 diabetic patients aged 35–55 years participating in the World Health Organization MultinationalStudy of Vascular Disease in Diabetes has been followed up from 1975 to 1987. Excess mortality,compared with the background population, was assessed in terms of standardized mortalityratios (SMRs) for each of the 10 international cohorts. The relationship between excess mortalityand proteinuria/hypertension was examined by diabetes type and sex. RESULTS SMRs were in general higher in patients with IDDM (ranging from 188 to 686 formen and from 336 to 790 for women) than with NIDDM (from 138 to 370 for men and from 126to 435 for women). For both diabetes types and in both sexes, SMRs decreased with increasingage and increased with increasing diabetes duration. Patients with both hypertension and proteinuria experienced a strikingly high mortality risk: 11-fold for men with IDDM and 18-fold forwomen with IDDM and 5-fold for men with NIDDM and 8-fold for women with NIDDM. Evenin the absence of proteinuria and hypertension, SMRs were significantly increased in both IDDM(284 men and 360 women) and NIDDM (192 men and 236 women) patients. CONCLUSIONS Considerable international differences were found not only in mortalityrates for the two types of diabetes but also in the extent of excess mortality among centers. IDDM patients had a high excess mortality in comparison with the general population. The significantexcess mortality was demonstrated even in patients without proteinuria and without hypertension for both sexes and diabetes types.