Objectives: Posttraumatic stress disorder (PTSD) has been linked to risky sexual behavior (RSB). However, little is known regarding the role of impulsivity in this relation among college students. Participants: The present study examined the moderating role of impulsivity dispositions on the relation between PTSD symptoms and past-year RSB in a sample of 221 trauma-exposed undergraduate students (77.4% female). Results: Two separate negative binomial regression models examined each impulsivity disposition's unique moderating effect on the association between PTSD symptoms and high risk/casual sex. In the high risk model, significant interactions were found for the urgency dispositions, (lack of) premeditation and (lack of) perseverance, though the pattern of these relations differed across these dispositions. Only positive main effects for negative urgency and (lack of) premeditation emerged in the casual sex model. Conclusions: The present study expands on the limited literature on the role of impulsivity in the relation between PTSD and RSB in trauma-exposed college students.