While prior research shows relationships among childhood victimization, poor emotion regulation, and adult psychopathology, less is understood about the mechanisms that govern these relationships. We assessed childhood victimization, adulthood trauma, negative mood dysregulation, and posttraumatic stress disorder (PTSD) severity in a sample of 142 retired police officers. We conducted analyses to determine whether difficulties with negative mood regulation (NMR) mediated the relationship between childhood victimization and adult PTSD severity, or whether adult PTSD severity mediated the relationship between childhood victimization and poor NMR. We found that retrospectively reported childhood victimization was associated with poorer NMR in adulthood and more severe adult PTSD symptoms. Elevated PTSD symptom severity was associated with diminished NMR. Our main finding was that PTSD severity partially mediated the relationship between childhood victimization and adult negative mood dysregulation. These findings are consistent with the interpretation that childhood victimization elevates risk for adult psychopathology, which in turn potentiates adult emotion dysregulation. However, the findings are limited by: (1) retrospective self-report assessments of childhood trauma, (2) data drawn from a narrow population of adult trauma survivors (police), and (3) the cross-sectional design. The findings nonetheless suggest future prospective and intervention studies.