IMPORTANCE: Maternal posttraumatic stress disorder (PTSD) may be associated with increased risk for child maltreatment and child exposure to traumatic events. Exposure to multiple traumatic events is associated with a wide range of adverse health and social outcomes in children. OBJECTIVE: To examine the association of probable maternal depression, PTSD, and comorbid PTSD and depression with the risk for child maltreatment and parenting stress and with the number of traumatic events to which preschool children are exposed. DESIGN: Cross-sectional observational design.We used analysis of variance to determine whether probable maternal psychopathology groups differed on child maltreatment, parenting stress, and children's exposure to traumatic events. Hierarchical regression analyses were used to examine the unique and interactive effects of depression and PTSD severity scores on these outcomes. SETTING: Urban pediatric primary care outpatient clinic. PARTICIPANTS: Ninety-seven mothers of children aged 3 to 5 years. EXPOSURE: Pediatric primary care visit. MAIN OUTCOMES AND MEASURES: Probable maternal depression and/or PTSD, parenting stress, child exposure to traumatic events, and child maltreatment. RESULTS: Mothers with probable comorbid PTSD and depression reported greater child-directed psychological aggression and physical assault and greater parenting stress. The children of mothers with PTSD (mean number of events the child was exposed to, 5.0) or with comorbid PTSD and depression (3.5 events) experienced more traumatic events than those of mothers with depression (1.2 events) or neither disorder (1.4 events). Severity of depressive symptoms uniquely predicted physical assault and neglect. Symptom scores for PTSD and depression interacted to predict psychological aggression and child exposure to traumatic events. When PTSD symptom severity scores were high, psychological aggression and the number of traumatic events children experienced rose. Depressive symptom severity scores predicted the risk for psychological aggression and exposure to traumatic events only when PTSD symptom severity scores were low. CONCLUSIONS AND RELEVANCE: Children of mothers with PTSD are exposed to more traumatic events. Posttraumatic stress disorder is associated with an increased risk for child maltreatment beyond that associated with depression. Screening and intervention for maternal PTSD, in addition to maternal depression, may increase our ability to reduce children's exposure to traumatic stress and maltreatment.