This study explored whether youth involved in joint service systems differed from single-agency users in terms of types of crimes committed and clinical functioning. Data from 4,924 youth involved in one county's public mental health and juvenile justice service systems were examined. Twenty percent of those youth receiving mental health services had recent arrest records, and 30% of youth arrested received mental health services. Of all youth arrested in the county, mental health service users had more arrests than non-mental health service users. A subsample of 94 mental health service users with arrests was matched on demographics with 94 mental health service users without arrests. Youth with arrests had a higher frequency of conduct disorder, higher Child Behavior Checklist Externalizing and Total Problem Scale scores, and more functional impairment on the Child and Adolescent Functional Assessment Scale as compared to youth without arrests. Implications for behavioral health service delivery were discussed.