The Scrambled Sentences Task (SST) is a robust measure of interpretational processes in psychopathology. However, there is little evidence of its utility as a measure of dysfunctional appraisals (DAs) in relation to traumatic or negative life events. We therefore developed a novel SST in the context of trauma and Posttraumatic Stress Disorder (PTSD), and examined its psychometric properties including con- and divergent validity and 2-week test-retest reliability via an online study. Our sample (T1: N = 214, T2: N = 145) included participants who reported a potentially traumatic negative life event that was still experienced as distressing. We found high correlations between the novel SST and both PTSD-related symptoms and self-report measures of DAs, indicating good convergent validity. Further, both internal consistency and retest-reliability were good. However, we also found large correlations with symptoms of depression, and moderate correlations with symptoms of other disorders (e.g., eating disorders), indicating limitations to the SST’s divergent validity. Finally, the SST did not explain unique variance in PTSD-related symptoms above self-report measures. Overall, the results demonstrate the promise of the SST being a valid and reliable tool to assess DAs in the context of traumatic life events. Further research should aim to improve the specificity with which the SST assesses trauma-related DAs and investigate the relationship between the SST and self-report measures of DAs.