High rates of co-occurring posttraumatic stress disorder (PTSD) have been found among patients receiving treatment for substance use disorders (SUD), and there is evidence that this particular co-occurrence is associated with negative SUD treatment outcomes. Thus, there is utility in establishing the role of psychological vulnerabilities related to PTSD within SUD populations, with the goal of ultimately informing targeted interventions and improving clinical outcomes. Anxiety sensitivity (AS) and emotional avoidance (EA) may be two important factors in this regard, as both have been found to demonstrate associations with posttraumatic stress in other clinical and nonclinical populations. To expand upon this literature, the current study examined the associations between AS and EA and PTSD symptom severity in a sample of traumatic event-exposed crack/cocaine dependent patients in residential SUD treatment (n = 62), as well as the extent to which EA mediated the relation between AS and PTSD symptom severity. As hypothesized, AS and EA were associated with PTSD symptom severity above and beyond the effects of gender and non-specific anxiety symptoms. However, the hypothesis that EA would mediate the relation between AS and PTSD symptom severity was only partially supported. Implications of these findings for understanding and treating co-occurring SUD-PTSD are discussed.