We examined the relationship between negative appraisal and posttraumatic stress disorder (PTSD) symptoms among adults diagnosed with severe mental illness (SMI). It was hypothesized that negative appraisals of the self, the world, and self-blame would have a positive and significant association with traumatic stress symptoms in a clinical sample of community clients diagnosed with an Axis I primary diagnosis of either severe major mood disorder or schizophrenia-spectrum disorder when controlling for gender, total lifetime trauma, substance abuse, and severity of symptoms of psychosis and depression. Multiple regression was employed to conduct a secondary analysis of clinical data from 291 community support clients who were receiving services from three community mental health centers. Results supported the main hypotheses that all three types of negative appraisal with respect to self, world/others, and self-blame were positively and significantly associated with PTSD symptoms. The authors recommend improvements in screening and intervention with trauma/PTSD, and fuller appreciation of the variable role of negative appraisal when conducting trauma/PTSD assessments.