Background: In 1955, an outbreak of arsenic poisoning caused by ingestion of arsenic-contaminated dry milk occurred in western Japan. We assessed the excess mortality among Japanese who were poisoned during this episode as infants.Methods: We identified and enrolled 6104 survivors (mean age at enrollment, 27.4 years) who had ingested contaminated milk when they were age 2 years or younger; they were followed until 2006 (mean duration of follow-up, 24.3 years). Death certificates of subjects who died between 1982 and 2006 were examined to calculate cause-specific standardized mortality ratios (SMRs) using the mortality rate among Osaka residents as the standard.Results: There was no significant excess overall mortality (SMR: 1.1, 95% confidence interval: 1.0-1.2). However, significant excess mortality in both sexes was observed from diseases of the nervous system (3.7, 1.9-6.2). Excess mortality from all causes of death decreased to unity beyond 10 years after study enrollment. The 408 men who were unemployed at the time of enrollment in the study had a significantly elevated risk of death from diseases of the nervous system (25.3, 10.8-58.8), respiratory diseases (8.6, 3.1-16.8), circulatory diseases (3.2, 1.6-5.2), and external causes (2.6, 1.4-4.1).Conclusions: As compared with the general population, survivors of arsenic poisoning during infancy had a significantly higher mortality risk from diseases of the nervous system.