Statistical analyses were used to derive and validate a statistical prediction instrument to determine combat-related posttraumatic stress disorder (PTSD) status. Participants were 1081 Vietnam veterans with and without combat-related PTSD. The statistical prediction instrument, which consisted of 12 well-known risk and resilience variables associated with PTSD, proved to be an accurate and efficient means of detecting PTSD among participants and compared well against other existing self-report measures of PTSD. The instrument's practical applications and its use in clinical appraisals of PTSD are discussed.