Differential survival associated with insulin-dependent diabetes mellitus (IDDM) was evaluated in a cross-country study using four population-based IDDM cohorts from Japan (n = 1,374), Israel (n = 610), Allegheny County, Pennsylvania (n = 995), and Finland (n = 5,144). For the purpose of this cross-country comparison, the Allegheny County cohort was taken to be representative of the United States. The mortality status as of January 1, 1990, was determined for all individuals who were diagnosed with diabetes at the age of less than 18 years between 1965 and 1979 and who were taking insulin at the time of hospital discharge. The results showed that the mortality experience for IDDM individuals in Japan and the United States was much worse than that in Finland and Israel. The age-adjusted mortality rates (per 100,000 person-years) for the four cohorts were 760 (Japan), 158 (Israel), 408 (Allegheny County), and 250 (Finland). By using the mortality data from Allegheny County, Pennsylvania, to extrapolate to the US IDDM mortality experience, the authors estimated 2,396 deaths among individuals with IDDM in the United States. It was calculated that 1,261 (53%) of these deaths would not have occurred in the United States given Finland's mortality rates. It is critical to determine why individuals with IDDM in the United States have a poorer outcome.