This study examines the effects of temperament on self-reported posttraumatic stress disorder (PTSD) symptoms from a convenience sample of US military service members (N=559). Previously deployed active duty service members completed anonymous questionnaires that included demographics, temperament, and PTSD measures. This study also examines demographic variables such as age, gender, ethnicity, race, education, and marital status, and service-related variables such as branch, grade, and years of military service for moderating effects. Results suggest a relationship between the temperament dimensions and PTSD symptoms in that the temperament dimensions of low mood quality, high levels of activity generally and during sleep, and low flexibility were found to predict high levels of self-reported PTSD symptoms. This is the first study incorporating temperament as a predictor of PTSD within a military population and provides the basis for future research in this area.