How many people suffer from posttraumatic stress disorders and related psychopathology after the experience of a traumatic life event? The majority of the studies into the psychological consequences of extreme stress has been focused on samples that consisted of patients and is therefore not equipped to provide an answer to the proposed question. This article is a systematic overview of studies of representative samples of people who experienced traumatic life events. Despite the screening of hundreds of publications only 25 studies were found which provided adequate data. Incidence findings of posttraumatic stress disorders and related disturbances are presented with regard to combat stress, natural disasters, acts of violence and accidents. The overview also provides information about the samples and the diagnostic instruments that were employed. The authors discuss the diversity of methodological problems that must be solved in order to get reliable and valid incidence data. These problems concern issues such as the random character of the sample, the non-response rate, the conceptualization of the disorder and the period between the study and the event. The article ends with general guidelines for future research and implications for mental health care.