Background: Maternal depression is a common condition among new mothers that can be associated with poor maternal health and negative consequences on infant health. Little research has been conducted to examine maternal depression, especially among military mothers, where unique conditions often exist. Using data from a large military cohort, this study prospectively examined the relationship between deployment experience before and after childbirth and maternal depression among U.S. servicewomen. Methods: The study included 1,660 female Millennium Cohort participants who gave birth during active duty service and completed baseline and follow-up questionnaires between 2001 and 2008. Maternal depression was assessed at follow-up using Primary Care Evaluation of Mental Disorders Patient Health Questionnaire criteria. Results: Deployment before childbirth, regardless of combat experience, and deployment without combat experience after childbirth did not increase the risk of maternal depression. Women who deployed and reported combat experience after childbirth were at increased risk for maternal depression compared with nondeployed women who gave birth (adjusted odds ratio [OR] 2.01, 95% confidence interval [CI] 1.17-3.43). Among the subgroup of female combat deployers, however, women who gave birth did not have a significantly increased risk for depression compared with those who did not give birth. Conclusions: Military women who deployed with combatlike experiences after childbirth were at increased risk for postdeployment maternal depression. The risk, however, appeared primarily related to combat rather than childbirth-related experiences.