Posttraumatic stress responses have been linked to a range of social-cognitive and sociodemographic factors. Rational emotive behaviour therapy suggests that responding to a traumatic life event with a set of irrational beliefs should play a crucial role in predicting the development of posttraumatic stress disorder (PTSD: Ellis in Overcoming destructive beliefs, feelings, and behaviours: new directions for rational emotive behaviour therapy, Prometheus Books, Amherst, 2001). The current study assessed the role of trauma-specific irrational beliefs in the prediction of clinically relevant posttraumatic stress responses, while controlling for a range of important sociodemographic factors. A sample of 313 trauma-exposed military and law enforcement personnel took part in the current study and were divided into two groups according to the intensity of reported PTSD symptomology. Results of the binary logistic regression indicated that trauma-specific Catastrophizing, Low Frustration Tolerance, and Depreciation beliefs, respectively, significantly predicted belonging to the group reporting strong symptoms of PTSD compared to those reporting mild symptoms of PTSD. These results provide important evidence of the role of irrational beliefs in posttraumatic stress responses and highlight the importance of considering context-specific variants of each irrational belief process.