Coverage of PTSD and posttraumatic illness epidemiology wisely begins with general caveats, such as the impact of priming questionnaire respondents on subsequent symptom endorsement. Major epidemiologic endeavors, such as the National Vietnam Veterans Readjustment Study, are described, and studies of other traumatic events, such as terrorist activities or natural disasters, are also reviewed. A table would help summarize the huge blur of incidence and prevalence rates.