Objective: A cross-cultural study was completed to evaluate differences in mortality patterns in four population cohorts in Japan; Israel; Allegheny County, Pennsylvania; and Finland. Research Design and Methods: Cases were diagnosed between 1 January 1965 and 31 December 1979. Mortality was determined as of 1 January 1985. There were 147 deaths occurring in the 8212 insulin-dependent diabetes mellitus (IDDM) patients in the four countries. A standardized protocol for assessing causes of death (cause-specific mortality) was developed; in this article, we report the causes. Results: Major overall mortality differences by country appeared, with IDDM subjects in Japan much more likely to die than in the other countries. In Japan, the elevated mortality was the result of acute diabetes-related complications and kidney disease. For all countries, mortality from acute diabetes-related complications accounted for a surprisingly high percentage of deaths (> 25% in each country). A larger percentage of cases in Finland died as a result of suicide than for the other three countries. Conclusions: The results suggest that there are major cross-country differences in cause-specific mortality and that much of the premature mortality associated with diabetes is potentially preventable.