Objective: People with posttraumatic stress disorder (PTSD) are at high risk for substance use, and PTSD is common among women experiencing intimate partner violence. Considering the effects of both PTSD and substance use, such as poorer treatment outcomes and greater health/behavior problems, women experiencing intimate partner violence are a high-risk, under-researched group. Methods: We utilized a micro-longitudinal study design to assess daily drug and alcohol use over 21 days among 41 women experiencing intimate partner violence recruited from the community. Results: Participants were about 45 years old (M = 45.1, SD = 8.5) and mostly African American (n = 32, 78%). Co-occurrence of drug and alcohol use was reported on 19.0% of days, while drug use alone occurred on 13.4% of days and alcohol use on 12.1%. Fifteen percent of participants met current PTSD criteria, with a mean symptom severity rating of 15.90 (SD = 10.94, range 0 to 47). Women with PTSD, compared to those without, were nearly 15 times more likely to have days of co-occurrence of drug and alcohol use (p = .037) and nearly 7 times more likely to have days of drug use alone (p = .044). Conclusions: These findings indicate that the combination of intimate partner violence and PTSD may make women especially prone to daily co-occurring drug and alcohol use or drug use alone. Further research is needed to explore this association and examine the need for integrated programs to support victims' health, prevent the development of substance use problems, and facilitate recovery from PTSD and substance use.