Background Death rates in military populations outside of combat are often lower than those in the general population. This study considers how this "healthy soldier effect" changes over time. Methods Standardized mortality ratios were used to compare changes in death rates relative to the Australian population in two large studies of Australian servicemen of the Korean War (n = 17,381) and the Vietnam War era (n = 83,908). Results The healthy soldier effect was most consistently observed in deaths from circulatory diseases. A large deficit in these deaths in the initial follow-up period (10-20 years) was observed before rates tended to rise to the level seen in the general population. There was no healthy soldier effect in deaths from external causes in enlisted personnel, and these death rates were significantly higher than expected in the initial follow-up period among Korean War veterans and regular Army veterans of the Vietnam War. Those selected for national service during the Vietnam War exhibited the strongest healthy soldier effect of all cohorts assessed. Conclusions Patterns of the healthy soldier effect over time varied markedly by study cohort and by cause of death studied. In a number of analyses, the healthy soldier effect was still apparent after more than 30 years of follow-up.