Abstract: Research has shown higher rates of trauma exposure and posttraumatic stress disorder (PTSD) among persons with severe mental illness (SMI). The aim of this study was to assess the prevalence of traumatic events and full and partial PTSD among people with SMI and their associations with trauma-related cognitions and depressive symptoms. A total of 122 persons with SMI were assessed for trauma exposure and PTSD. A subsample of 40 participants, 20 with PTSD and 20 without PTSD, were randomly selected, and their posttraumatic cognitions and depressive symptoms were assessed. The prevalence of traumatic events was 90%, and 19% met full diagnostic criteria for PTSD, and 20% had partial PTSD. The people with PTSD had more depressive symptoms and negative cognitions. PTSD in SMI is highly prevalent and underdiagnosed.