Objective: To examine the mediational significance of posttraumatic stress disorder (PTSD) and the development of eating disorder symptomatology following sexually traumatic experiences. Method: Seventy-one victims of sexual trauma and 25 control subjects completed interviews and questionnaires assessing eating disorder psychopathology and posttraumatic stress disorder symptomatology. Mediational analyses were conducted examining the relationships among trauma, posttraumatic stress, and eating disorder symptoms. Mediational significance was assessed by the drop in the overall correlation between trauma and eating disorder symptoms when PTSD symptoms were included in the regression model. Results: There is a significant association between a history of trauma and eating disorder symptoms. Also, there was a significant association between a history of trauma and posttraumatic stress disorder symptoms. Importantly, the relationship between trauma and eating disorder symptoms was significantly reduced when posttraumatic stress disorder symptoms were included in the regression analyses, indicating mediational significance of the posttraumatic stress construct. These findings were most pronounced for the physiological arousal and avoidance components of posttraumatic stress disorder. Discussion: The present findings support the idea that individuals who develop eating disorders after sexual trauma are likely to have experienced posttraumatic stress disorder symptomatology. These findings have significant implications for causal models of eating disorder onset in trauma victims. Furthermore, clinical interventions for traumatized eating disordered individuals may benefit from a focus on posttraumatic stress symptomatology. (Contains 2 tables.)