The Ontario Child Health Study (OCHS) described in the companion paper (1) confirms the fact that psychiatric disorders among children and adolescents are prevalent, that comorbidity and associated impairements are common and that only a minority of children are seen by any definite mental health or social service. The current assessment and treatment methods and the present service system leave the majority of children unserved. Children and their families suffer a good deal before they are adequately diagnosed and treated, and treatment service delivered on a one-by-one basis are expensive. The OCHS data, has, it follows, important implications for clinical work, for mental health service planning, for further research and for training in child and adolescent psychiatry. This paper does not address all the implications of the OCHS in these areas but does attempt to address those which follow from the summary of the OCHS data described in (1).