This article describes the psychometric properties of a novel questionnaire, i.e. the Trauma Relevant Assumptions Scale (TRAS). The added value of the TRAS over previous trauma relevant belief questionnaires is that the TRAS enables measuring valence and rigidity of beliefs simultaneously. Both aspects are thought to be predictive of the development of chronic PTSD symptoms. For the exploratory factor analysis, the TRAS was administered to 309 adult volunteers. Principal components analysis yielded two factors: Assumptions about Self and Assumptions about the World. The two-factor structure was confirmed in a sample of 185 traumatized individuals. The TRAS seems to be a valid and reliable instrument, which is strongly related to post-trauma symptoms and has good discriminative validity. Apart from research settings, the TRAS may also be suitable in therapeutic settings to identify the severity of dysfunctional assumptions, and to assess the progress in change from negative assumptions to more positive assumptions.