There is much interest in identifying people shortly after trauma exposure who will subsequently develop posttraumatic stress disorder (PTSD). This review outlines recent developments in early identification of trauma-exposed people who are at high risk for PTSD development, including the rationale, evidence, and limitations of the acute stress diagnosis as a predictor of chronic PTSD. The potential role of acute dissociative responses mediating development of PTSD is also reviewed. The available evidence suggests that whereas acute dissociation is an important factor in the acute stress response, many people develop PTSD in the absence of dissociative symptoms. The evidence suggests that dissociation needs to be considered in the context of other factors in the aftermath of trauma if optimal identification of high-risk individuals is to be achieved.