Child maltreatment is a reliable predictor of posttraumatic stress disorder (PTSD) symptoms. However, not all maltreated children develop PTSD symptoms, suggesting that additional mediating variables explain how certain maltreated children develop PTSD symptoms and others do not. The current study tested three potential mediators of the relationship between child maltreatment and subsequent PTSD symptoms: (a) respiratory sinus arrhythmia reactivity, (b) cortisol reactivity, and (c) experiential avoidance, or the unwillingness to experience painful private events, such as thoughts and memories. Maltreated (n = 51) and nonmaltreated groups (n = 59) completed a stressor paradigm, a measure of experiential avoidance, and a semistructured interview of PTSD symptoms. One year later, participants were readministered the PTSD symptoms interview. Results of a multiple mediator model showed the set of potential mediators mediated the relationship between child maltreatment and subsequent PTSD symptoms. However, experiential avoidance was the only significant, specific indirect effect, demonstrating that maltreated children avoiding painful private events after the abuse were more likely to develop a range of PTSD symptoms 1 year later. These results highlight the importance of experiential avoidance in the development of PTSD symptoms for maltreated children, and implications for secondary prevention and clinical intervention models are discussed.