Impulsivity is a key feature of opioid use disorder (OUD) and other psychiatric conditions, including posttraumatic stress disorder (PTSD). The relationship between disorders and impulsivity may be additive, such that individuals with multiple disorders exhibit greater impulsivity than those with a single disorder. However, the association between impulsivity, OUD, and PTSD is unclear. Accordingly, this study compared individuals with concurrent OUD and PTSD (OUD + PTSD; n = 55), OUD without PTSD (OUD-PTSD; n = 34), PTSD without OUD (n = 32), and healthy controls (HCs; n = 55) on the Short Urgency, Premeditation, Perseverance, Sensation Seeking, Positive Urgency Impulsive Behavior Scale (SUPPS-P), and the 27-item Monetary Choice Questionnaire (MCQ). With respect to the SUPPS-P, the OUD + PTSD, OUD-PTSD, and PTSD without OUD groups reported more impulsivity on the negative urgency, positive urgency, and lack of premeditation subscales compared to HCs (ps < .001). The OUD + PTSD group also reported greater negative urgency compared to the OUD-PTSD group (p = .001) and HCs (p < .001), but not the PTSD without OUD group (p = .07). Furthermore, participants with OUD + PTSD exhibited greater discounting of delayed rewards on the MCQ than those in the PTSD without OUD group and HCs (p's < .001). However, no significant differences were observed between the two OUD groups (p = .86). These results support impulsivity as a mechanism underlying both OUD and PTSD. Future research should examine whether interventions targeting impulsivity, emotion regulation, and delay discounting are associated with meaningful improvements in functioning among individuals with OUD and PTSD. (PsycInfo Database Record (c) 2022 APA, all rights reserved).