Young people with comorbid disorders (coexisting mental health and substance use disorders) present with particular issues that can be difficult for service providers, and for the community as a whole, to respond to. They tend to fall between the cracks of mental health services and substance use services, with the outcome often being ineffective treatment, or no treatment at all, for the young people concerned, and increasing conflict, ideological clashes and blame between agencies. There is urgent need for better communication and development of protocols between mental health services and substance use services for young people; both need to recognise and respect their differing expertise, develop coordinated treatment plans and convey this information to the wider helping services sector. Cross-training is necessary for professionals in the mental health and substance use fields. (Contains 1 table.)