Objectives Posttraumatic stress disorder PTSD and unhealthy alcohol use are commonly associated conditions. It is unknown whether specific symptoms of PTSD are associated with subsequent initiation of unhealthy alcohol use. Methods Data from the first 3 enrollment panels n 151,567 of the longitudinal Millennium Cohort Study of military personnel were analyzed 2001-2012. Complementary log-log models were fit to estimate whether specific PTSD symptoms and symptom clusters were associated with subsequent initiation of 2 domains of unhealthy alcohol use risky and problem drinking experience of 1 or more alcohol-related consequences. Models were adjusted for other PTSD symptoms and demographic, service, and health-related characteristics. Results Eligible study populations included those without risky n 31,026 and problem drinking n 67,087 at baseline. In adjusted analyses, only 1 PTSD symptom irritabilityanger was associated with subsequent increased initiation of risky drinking relative risk RR 1.05, 95 confidence interval CI 1.001.09 at least 3 years later. Two symptom clusters dysphoric arousal RR 1.17, 95 CI 1.111.23 and emotional numbing RR 1.30, 95 CI 1.221.40 and 5 symptoms restricted affect RR 1.13, 95 CI 1.081.19, sense of foreshortened future RR 1.12, 95 CI 1.061.18, exaggerated startle response RR 1.07, 95 CI 1.011.13, sleep disturbance RR 1.11, 95 CI 1.071.15, and irritabilityanger RR 1.12, 95 CI 1.071.17 were associated with subsequent initiation of problem drinking. Conclusions Findings suggest that specific PTSD symptoms and symptom clusters are associated with subsequent initiation of unhealthy alcohol use.