The authors describe historical clinical reports that preceded the development of criteria for posttraumatic stress disorder (PTSD) and influenced the formation of PTSD in DSM-IV. These reports were identified from extensive search of 19th- and 20th-century American and European medical literature. Relevant findings from the most representative reports are described and discussed. Since the mid-19th century, clinical syndromes resembling PTSD have been described. However, understanding of PTSD has been complicated by questions of nomenclature, etiology, and compensation. Nomenclature placed PTSD syndromes under existing psychiatric disorders: traumatic hysteria, traumatic neurasthenia, or traumatic neurosis. Etiological issues have been concerned often solely with organic factors, pre-existing personality impairments, intrapsychiatric conflicts, and social factors. Only after World War II and the concentration camp experiences did the role of severe trauma in PTSD become recognized. Even though controversy remains, much progress in understanding PTSD has been made.