Posttraumatic stress disorder (PTSD) and alcohol misuse are commonly co-occurring problems in active-duty service members (SMs) and veterans. Unfortunately, relatively little is known about the temporal associations between these problems in the acute period following exposure to combat stressors. Discerning the temporal associations between these problems across the deployment cycle could inform prevention and treatment efforts. In this study, we examined the association between PTSD symptom severity and problem alcohol use in a large cohort of United States Marines (n = 758) evaluated prior to deployment and approximately 1, 5, and 8 months postdeployment. Results indicate that problem alcohol use was associated with a subsequent exacerbation of PTSD symptoms between the 1st and 2nd and 2nd and 3rd postdeployment assessments. PTSD symptom severity was associated with increased problem alcohol use between the 1st and 2nd postdeployment assessments. These findings suggest that problem drinking may lead to new onset or worsening of PTSD symptoms over time and that SMs with greater PTSD symptom severity upon returning from deployment may increase alcohol use in the weeks immediately following homecoming. (PsycINFO Database Record (c) 2019 APA, all rights reserved)