Objective Comorbidity among eating disorders, traumatic events, and post traumatic stress disorder (PTSD) has been reported in several studies. The main objectives of this study were to describe the nature of traumatic events experienced and to explore the relation between PTSD and anorexia nervosa (AN) in a sample of women. Methods Eight hundred twenty-four participants from the National Institutes of Health funded Genetics of Anorexia Nervosa Collaborative Study were assessed for eating disorders, PTSD, and personality characteristics. Results From a final sample of 753 women with AN, 13.7% (n=103) met DSM-IV criteria for PTSD. The sample mean age was 29.5 years (SD=11.1). In pairwise comparisons across AN subtypes, the odds of having a PTSD diagnosis were significantly lower in individuals with restricting AN (RAN) than individuals with purging AN without binge eating (PAN) (OR=0.49, 95% CI=0.30, 0.80). The majority of participants with PTSD reported the first traumatic event before the onset of AN (64.1%, n=66). The most common traumatic events reported by those with a PTSD diagnosis were sexual related traumas during childhood (40.8%) and during adulthood (35.0%). Conclusions AN and PTSD do co-occur and traumatic events tend to occur prior to the onset of AN. Clinically, these results underscore the importance of assessing trauma history and PTSD in individuals with AN and raise the question of whether specific modifications or augmentations to standard treatment for AN should be considered in a subgroup to address PTSD-related psychopathology.