Abstract: Objective: Posttraumatic stress (PTS) symptoms and problematic alcohol use (e.g., binge drinking and alcohol-related problems; ARP) commonly co-occur following stressors and traumatic events. Ecological momentary assessment methods can clarify the functional relationships between these conditions. Methods: Twenty-five trauma-exposed combat veterans with pre-pandemic heavy drinking histories completed three daily smartphone surveys for four weeks, assessing binge drinking, ARP, PTS symptoms, and positive and negative affect. Within-person multi-level models assessed PTS and alcohol relationships, covarying for affect and demographics. Results: Within-person variation in PTS was inversely associated with binge drinking but not associated with ARP after adjustment for interindividual heterogeneity. Within-person variation in ARP was not associated with PTS after adjustment for interindividual heterogeneity. The covariate of negative affect was positively associated with ARP and PTS. Conclusions: Findings suggest negative affect, rather than PTS, has the strongest association with variation in ARP symptoms in this at-risk sample. There was also evidence of individual differences in the strength and direction of effects.