Chronic childhood illness, disability, and psychosocial problems are receiving major attention in current pediatric care. Much of the evidence associating chronic physical problems and mental health and adjustment problems has come from clinic-based studies and is often inconsistent in its conclusions. This paper reports the findings of the Ontario Child Health Study, an epidemiologic survey of 3,294 children 4 to 16 years of age in the general community, concerning the relationship of psychiatric disorders and social adjustment problems among children with chronic illness, medical conditions, and long-term disability in contrast to children free of chronic physical health problems. Age- and sex-adjusted risks for psychiatric disorders and social problems, compared with those for healthy peers, were calculated: children with both chronic illness and associated disability were at greater than threefold risk for psychiatric disorders and considerable risk for social adjustment problems. Children with chronic medical conditions, but no disability, were at considerably less risk: about a twofold increase in psychiatric disorders but little increased risk for social adjustment problems was observed. A relative underuse of specialized mental health services by children who might benefit supports the opinion that all physicians in the community who care for children with chronic health problems should become skilled in the recognition of existing or incipient mental health and social problems and familiar with preventive and treatment approaches that may lessen the excessive burden of psychosocial problems among those with chronic ill-health.