Trauma involving violation of trust, or betrayal trauma, plays a significant role in the lifetime trajectories of homeless adults. This study investigates this type of trauma and posttraumatic stress disorder (PTSD) symptom severity in the chronically homeless population. The sample consisted of 77 adults with a history of trauma and chronic homelessness in Melbourne, Australia. Using the Composite International Diagnostic Interview Traumatic Events Questionnaire, participants nominated their worst traumatic event and self-reported if their trust was violated as a result of that trauma. PTSD symptom severity was assessed by the 6-item PTSD Checklist. Forty percent of the sample reported violation of trust occurred in their worst trauma. Within this group, 80.6% screened positive for PTSD, compared to 50.0% of those whose worst trauma had not involved a trust violation (p = .006). The violation of trust group presented with significantly more severe PTSD symptoms, in comparison to the group without violation of trust during their worst trauma, controlling for gender, age of worst trauma, cumulative trauma, and psychological distress (p = .020). The findings highlight the importance of providing trauma-informed care and trauma-specific treatment for chronically homeless adults.