This prospective, longitudinal study investigated risk factors in the development of psychological ill health and posttraumatic stress symptoms in a sample of 223 junior police officers. Participants were assessed using a self-report methodology during training and again 12 months later on a range of personality, trauma exposure, and symptom measures. Risk factors for general psychological ill health at phase 2 of the research were found to comprise mostly stable, preexisting characteristics such as personality style, gender, and trait dissociation. Conversely, specific traumatic stress symptoms were more heavily influenced by experiences in the intervening 12 months, such as severity of incident exposure and peritraumatic dissociation. The implications for differential intervention are discussed.