The nature of incurring brain injuries, such as traumatic brain injury (TBI) and subarachnoid haemorrhage (SAH), has prompted research which considers the development of posttraumatic stress disorder (PTSD) after such events. However, despite the psychological nature of PTSD, previous reviews have focused upon the injury-related and neurological characteristics of its prevalence in TB!. Consequently, the first paper aimed to systematically review the quantitative research relating to the psychological and psychosocial variables associated with PTSD symptoms after TBI in civilian adults. A detailed search retrieved 28 articles, which subsequently underwent a thorough quality assessment, as well as the extraction of relevant data. The results highlighted several psychological and psychosocial variables associated with PTSD after TB!. Moreover, the results demonstrated the importance of addressing psychological and psychosocial factors within psychological therapy of PTSD after TB!. Limitations of the literature are discussed, including the fact that little research has been framed within psychological theory. In light of this, the second paper aimed to examine the psychological processes underlying PTSD after brain injury. Moreover, a study was conducted which assessed whether metacognitive processes correlated with, and predicted, posttraumatic stress symptom (PTSS) severity in individuals who had sustained a TBI (n = 47) or SAH (n = 93). Participants completed questionnaires related to demographic, clinical, social support, and metacognitive variables. Correlation analyses and a hierarchical multiple regression analysis demonstrated that metacognitive predictors correlated with PTSS severity, and were able to explain an additional and significant amount of its variance after TBI and SAH. Moreover, the results provide support that metacognitive variables are associated with PTSS after brain injury. Finally, the third paper consists of a critical review, which offers a reflective discussion on the role of clinical psychology within the paradigm of quantitative research that utilises diagnostic frameworks.