Health and illness beliefs - sometimes more aptly described as myths - frequently contribute to stuckness and dysfunction in families coming to Child and Adolescent Mental Health Services. This article examines the influence of some commonly presenting medical beliefs/attitudes on family and individual functioning. Misperceptions and myths about illness, although particularly common in children, are probably underrecognized and thus are given special emphasis. An attempt is made to explore the origins of dysfunctional health beliefs in terms of culture, previous family and medical history, and problems in relationships with health professionals. Details are given of some ways to tackle these beliefs in therapy employing systemic and cognitive approaches. These include the use of curiosity, scientific partnerships, the `as though' technique and genograms. A step towards prevention would be better training in psychological aspects of medicine for health professionals in all specialities, in addition to improving education for the public in health matters.