Background A deficit in the ability to inhibit fear has been proposed as a biomarker of posttraumatic stress disorder (PTSD). Previous research indicates that individuals with PTSD show reduced inhibition‐related activation in rostral anterior cingulate cortex (rACC). The goal of the current study was to investigate differential influences of an early environmental risk factor for PTSD—childhood maltreatment—on inhibition‐related brain function in individuals with PTSD versus trauma‐exposed controls. Methods Individuals with PTSD (n = 37) and trauma‐exposed controls (n = 53) were recruited from the primary care waiting rooms of an urban public hospital in Atlanta, GA. Participants completed an inhibition task during fMRI, and reported childhood and adult traumatic experiences. The groups were matched for adult and child trauma load. Results We observed an interaction between childhood maltreatment severity and PTSD status in the rACC (P < .05, corrected), such that maltreatment was negatively associated with inhibition‐related rACC activation in the PTSD group, but did not influence rACC activation in the TC group. Rostral ACC activation was associated with inhibition‐related task performance in the TC group but not the PTSD group, suggesting a possible contribution to stress resilience. Conclusions Findings highlight individual differences in neural function following childhood trauma, and point to inhibition‐related activation in rostral ACC as a risk factor for PTSD.