INTRODUCTION: General population studies show child maltreatment is associated with a range of mental disorders including mood, anxiety and substance use disorders. Numerous studies have also documented high rates of psychiatric comorbidity among opioid dependent persons; child maltreatment may be an important antecedent to the complex presentations of this population. The present study compares the association of child maltreatment and two highly comorbid mental disorders (posttraumatic stress disorder (PTSD) and major depressive episode (MDE)) among a sample of opioid-dependent persons and a matched control group. METHOD: Cases were recruited from opioid pharmacotherapy services in the greater Sydney area and surrounding regional centres. Controls (lifetime opioid use less than five times) were recruited via advertisements in stress press, flyer hand-outs in public spaces, and letter-box drops in low income areas. Controls were frequency matched to cases on age, gender, and employment. Retrospective self-report measures of child maltreatment, substance dependence, lifetime trauma exposure, early childhood risk factors, and lifetime PTSD and MDE were assessed via face-to-face interviews. RESULTS: Child maltreatment is highly prevalent in this sample. Opioid-dependent cases had a higher prevalence and greater severity of some types of child maltreatment compared to non-opioid-dependent controls. Overall, similar associations between child maltreatment and PTSD and MDE were found for both cases and controls. Sexual and emotional abuse were significant risk factors for both disorders; physical abuse was a significant risk factor for PTSD among males only. Severity of maltreatment was an important determinant of risk for PTSD but not MDE. DISCUSSION: These findings suggest the following: 1) assessment of child maltreatment (including sexual, physical, emotional abuse and neglect) among persons presenting to treatment for opioid dependence is warranted; and 2) there is a need for ongoing assessment and management of comorbid PTSD and MDE.