Background: The stresses and life changes associated with migration may have harmful long-term health effects, especially for mental health. These effects are exceedingly difficult to establish, because migrants are typically a highly selected group.

Methods: We examined the impact of migration on health using naturally occurring historical events. In this article, we use the forced migration of 11% of the Finnish population after WWII as such a natural experiment. We observed the date and cause of death starting from 1 January 1971 and ending in 31 December 2010 for the cohort of 242,075 people. Data were obtained by linking individual-level data from the 1950 and 1970 population censuses and the register of death certificates from 1971 to 2010 (10% random sample). All-cause and cause-specific mortalities were modeled using Poisson regression.

Results: Models with full adjustment for background variables showed that both all-cause mortality (RR 1.03, 95% CI 1.01, 1.05), and ischemic heart disease mortality (RR 1.11, 95% CI 1.08, 1.15) were higher in the displaced population than in the nondisplaced population. Suicide mortality was lower (RR 0.77, 95% CI 0.64, 0.92) in displaced than in the general population.

Conclusions: In our long-term follow-up study, forced migration was associated with increased risk of death due to ischemic heart diseases. In contrast, lower suicide mortality was observed in association with forced migration 25 years or more.