This study assesses the multidimensional structure of traumatic events as perceived by police officers and investigates individual differences in the scaling of such perceptions. Forty-two police officers with posttraumatic stress disorder (PTSD) and 40 officers without PTSD were given descriptions of critical incidents they were likely to encounter at work. They sorted these on the basis of similarity and rated them on 15 descriptive scales. The two groups were comparable in terms of relevant background characteristics. PTSD was diagnosed with the Structured Interview (SI-PTSD). The similarity data were subjected to individual differences multidimensional scaling analysis [Carroll and Chang, Psychometrika 35 (1970) 283]. The objective was, first, to identify the basic cognitive dimensions of psychological trauma that police officers use in discriminating between common critical incidents and, second, to test whether officers with and without PTSD apply such dimensions differently when interpreting critical incidents. The same three-dimensional solution was obtained for both groups: (1) emotional reactivity; (2) vulnerability and physical integrity; and (3) moral responsibility. Significant differences were found between the PTSD and non-PTSD groups in the salience of Dimension 2. Results are discussed with reference to other studies that address the meaning and interpretation of traumatic events. Implications for the conceptualization and assessment of trauma and PTSD are outlined.