We undertook a secondary data analysis to study issues relevant to co-occurring mental health and substance disorder in a combined sample of offenders (N = 3,197). Using the Personality Assessment Inventory, we compared the frequency of depressive, traumatic stress, and personality disorder symptom elevations across offenders with and without substance problems, identified the extent to which co-occurring problems were accompanied by risk factors for suicide and aggression, and tested for gender differences. Offenders with substance problems were more likely than others to have increased mental health problems and risk factors for suicide or aggression. Women with substance problems, compared with men, had higher depression, traumatic stress, and borderline features, in addition to lower antisocial features. The frequency with which suicide and aggression risk factors were associated with mental health problems was generally similar across men and women. Measurement issues relevant to co-occurring disorder and risk assessment are discussed.