The co-occurrence of posttraumatic stress disorder (PTSD) and substance use disorders (SUDs) is associated with greater risk for suicidal behavior than either disorder alone. Research highlights the relevance of PTSD symptoms in particular to suicide risk within this population. Research has also provided support for an association between distress tolerance (DT) and both PTSD symptoms and suicidal behavior. This study examined the role of DT in the relationship between PTSD symptom severity and suicidal behavior in a sample of 164 SUD inpatients with a history of Criterion A traumatic exposure. Results indicated that DT moderated the relationship between PTSD symptoms (overall, re-experiencing, and hyperarousal) and medically attended suicide attempts, with the magnitude of the relationship increasing at higher levels of DT.