Major cross-country differences in risk of dying for people with IDDM. Diabetes Epidemiology Research International Mortality Study Group. OBJECTIVE: Little is known concerning global differences in the risk of premature death for individuals developing youth-onset insulin-dependent diabetes mellitus (IDDM). The Diabetes Epidemiology Research International Study was developed to examine the mortality patterns of four population-based cohorts of IDDM cases from Allegheny County, Pennsylvania (n = 1000), Finland (n = 5146), Israel (n = 681), and Japan (n = 1428). RESEARCH DESIGN AND METHODS: All subjects were diagnosed as having diabetes, were less than 18 yr old at onset, were taking insulin at the time of hospital discharge, and were diagnosed between 1 January 1965 and 31 December 1979. The living status as of 1 January 1985 was determined. RESULTS: Overall, there were 182 deaths. Life-table analysis revealed that at 20-yr duration of diabetes, 5.5% of the cohort had died in Allegheny County in contrast to only 3.1% in Finland and 4.6% in Israel (P less than 0.01). Follow-up for an additional 3 yr in the United States and Finland revealed major differences in the 30- to 39-yr age-group, with 3.9 times greater premature mortality in the U.S. cohort compared with the Finnish group (overall mortality 2.3 vs. 0.6%, respectively). The Japanese cohort was developed in a somewhat different manner than the other three; therefore, the populations of the U.S., Finland, and Israel were reconfigured to make them directly comparable to that of Japan. The Japanese cohort exhibited markedly higher age-adjusted mortality rates (n/100,000 person-yr of diabetes) than the other three (Japan 681, U.S. 230, Finland 171, and Israel 131). CONCLUSIONS: These data indicate that young adult IDDM subjects are at an increased risk of premature death, there are differences in the mortality risk across countries, and both the U.S. and Japan have the major problem of an apparently excessive premature death rate among young people who have diabetes. 