Abstract: Alcohol abuse is associated with unique negative mental, physical, interpersonal, and occupational outcomes in the military. It is also often linked with traumatic combat exposure and posttraumatic stress disorder (PTSD) in an effort to relieve PTSD symptoms, in accordance with Conger’s (1956) “self-medication hypothesis”. Furthermore, younger military personnel tend to be more likely than older members to abuse alcohol, which may be explained, at least in part, by Winick’s (1962) “maturing out” hypothesis, which attributes the decline in alcohol abuse with age to the increased demands and responsibilities of adulthood roles, which do not accord with alcohol abuse. The current study investigated these theories simultaneously in a sample of Canadian military personnel (n = 15,832) surveyed 60 to 180 days upon return from deployment in support of the mission in Afghanistan. All unconditional effects were in the expected direction: greater combat exposure was significantly associated with greater PTSD symptomatology, which was in turn related to greater alcohol abuse. Alcohol abuse also decreased significantly in relation to increasing age. Additionally, a moderated mediation indicated that the association between combat exposure and alcohol abuse was partially mediated by PTSD symptoms, and this association was strongest among the youngest participants. These findings support both the self-medication and the maturing-out hypotheses of alcohol abuse, and highlight the importance of military education on effective coping strategies and awareness of available mental health resources, particularly among certain populations.