Since 2001, the US military has increasingly relied on National Guard and reserve component forces to meet operational demands. Differences in preparation and military engagement experiences between active component and reserve component forces have long suggested that the psychiatric consequences of military engagement differ by component. We conducted a systematic review of prevalence and new onset of psychiatric disorders among reserve component forces and a meta-analysis of prevalence estimates comparing reserve component and active component forces, and we documented stage-sequential drivers of psychiatric burden among reserve component forces. We identified 27 reports from 19 unique samples published between 1985 and 2012: 9 studies reporting on the reserve component alone and 10 reporting on both the reserve component and the active component. The pooled prevalence for alcohol use disorders of 14.5% (95% confidence interval: 12.7, 15.2) among the reserve component was higher than that of 11.7% (95% confidence interval: 10.9, 12.6) among the active component, while there were no component differences for depression or post-traumatic stress disorder. We observed substantial heterogeneity in prevalence estimates reported by the reserve component. Published studies suggest that stage-sequential risk factors throughout the deployment cycle predicted alcohol use disorders, post-traumatic stress disorder and, to a lesser degree, depression. Improved and more standardized documentation of the mental health burden, as well as study of explanatory factors within a life-course framework, is necessary to inform mitigating strategies and to reduce psychiatric burden among reserve component forces.