Objective: The co-occurrence of posttraumatic stress disorder (PTSD) and alcohol use disorder (AUD) is common. Individuals with PTSD/AUD commonly drink to cope with PTSD symptoms, which maintains PTSD/AUD, and may result in increased craving for alcohol. Negative affect is implicated in negative reinforcement models of craving. Further, Emotional Processing Theory posits that posttraumatic cognitions lead to the experience of negative affect, which may result in increased craving in PTSD/AUD. The current study aims to advance the understanding of craving in PTSD/AUD by evaluating if specific posttraumatic cognitions (e.g., cognitions about the self, world, and self-blame) are associated with increased negative affect, and whether higher negative affect is associated with heightened craving. Methods: Three separate simple mediation models were utilized to test if negative affect mediated the relationship between each specific posttraumatic cognition type and craving among 136 treatment-seeking veterans with PTSD/AUD. Results: We found that negative affect mediated the association between all posttraumatic cognition types and craving. Specifically, viewing oneself as being unable to handle PTSD-related distress, viewing the world as very dangerous, and blaming oneself for one's role in a traumatic event were all associated with increased negative affect, which was related to higher craving. Conclusions: Given that posttraumatic cognitions improve via trauma-focused treatment for PTSD, future work should evaluate whether improvements in posttraumatic cognitions via trauma-focused treatment lead to decreased negative affect and craving in PTSD/AUD.