Introduction: Although there are several studies dealing with early deaths due to mustard gas exposure, few studies have evaluated the delayed pattern of death in veterans suffering wartime exposure. This study was conducted to estimate the overall and cause-specific mortality rates and the proportion of each cause of death in deceased mustard-exposed veterans.Methods: A retrospective mortality study was carried out from 1986 to 2003 on all death certificates in the Janbazan Organization; demographic, war related and medical data were extracted from the subjects files. Causes of death, having been established by the death commission, were categorized as disease, trauma, suicide, homicide and gas exposure. Overall and cause - specific delayed mortality rates were associated with mustard.Results: Of 34,000 participants, 1,005 died within the period of the study. The overall mortality rate was 19.07 per 10,000 people each year. The most frequent cause of death was disease (72.2%), followed by trauma (16.1%), suicide (2.3%) and homicide (0.8%). In 2.8%, the cause of death was undetermined. 12.1% of all the deaths were due to mustard gas exposure. Conclusion: Exposure to mustard gas is not associated with high mortality in the late phase.