Recent cognitive models stress the impact that negative appraisals have on the maintenance of posttraumatic stress disorder (PTSD). The aim of this study was to investigate the role of posttraumatic negative cognitions in 110 survivors of motor vehicle accidents (MVAs) and to examine the effect of cognitive-behavioral treatment on negative appraisals in a sample of 42 patients with full or sub-syndromal PTSD. We investigated whether posttraumatic negative cognitions predicted PTSD diagnosis and symptom severity, and whether treatment-related changes in negative appraisals were associated with PTSD symptom reduction. Negative posttraumatic cognitions were significantly associated with PTSD diagnosis and severity, and explained 54% of the variance of the PTSD severity. Furthermore, treatment-related reductions in negative appraisals about the self were highly associated with PTSD-symptom-reduction. Our results raise question about whether there are factors that make the self more vulnerable in some people but not in others.