Childhood maltreatment increases risk for Posttraumatic Stress Disorder (PTSD). Maladaptive patterns of attention to threat-related stimuli warrant examination as possible contributing risk factors. It remains unclear whether persistent threat-processing biases are differentially apparent in adults who were maltreated as children and either did, or did not, develop later PTSD. The present study examined associations among attention bias, childhood maltreatment, and PTSD in adults. We hypothesized that attentional bias toward threat significantly mediates associations between childhood maltreatment and adult PTSD symptoms. 183 adults with and without childhood maltreatment histories participated in this study, which involved completion of a range of clinical measures; attention bias was measured by the Dot Probe task. We found that attention bias toward happy faces partially mediated the relationship between childhood maltreatment and PTSD avoidance and numbing symptoms. Childhood maltreatment, happy face attention bias, and perceived racially discriminative experiences all accounted for significant variance in PTSD symptoms.