This study examined use of mental health services by 947 high-risk youths in a publicly funded system of care to determine how single and comorbid diagnostic profiles (psychiatric and substance use disorders) were associated with use of a variety of types of formal and informal services. Use of professional services was most likely for youths with non-substance use psychiatric disorders, those with comorbid disorders, and those for whom high caregiver strain was reported. Use of informal services, such as peer support groups, was most likely for youths with substance use disorders, those with comorbid disorders, and those who had had police contact. Unmet need for mental health services was greatest among youth with substance use disorders only.