Abstract: BACKGROUND: To compare cause-specific mortality between an occupational cohort of U.S. service members and veterans and the general civilian adult population. METHODS: Dates and cause of death of deceased Millennium Cohort Study participants from 2001 to 2018 were extracted from federal and military databases. Standardized mortality ratios (SMRs) were calculated for cause-specific mortality compared with the general population overall and by sex and deployment history. RESULTS: Among 201,618 participants, 3,017 (1.5%) had a recorded cause of death by December 31, 2018. Compared with the U.S. general population, deaths due to natural causes (SMR = 0.36; 95% CI: 0.34-0.38), accidents (SMR = 0.47; 95% CI: 0.44-0.51), and homicides (SMR = 0.22; 95% CI: 0.17-0.29) were lower among service members and veterans. When stratified by sex, deaths by suicide overall were higher for military women (SMR = 1.65, 95% CI: 1.31-2.05) compared with women in the general U.S. population but not for men (SMR = 0.96, 95% CI 0.87-1.05). Deaths from suicide by firearms were elevated for both military women (SMR = 2.83, 95% CI: 2.04-3.82) and men (SMR = 1.33, 95% CI: 1.18-1.49) compared to the U.S. general population. CONCLUSIONS: Service members and veterans had lower overall mortality but higher mortality attributed to suicide by firearms compared with the general U.S. general population. Military women specifically had higher mortality rates from suicide overall. These findings warrant increased attention to reducing suicide deaths in military populations.