Psychological and physical (somatic) symptoms are closely interconnected, and somatisation (Box 12.1) is commonly seen in both primary and secondary care settings. Somatic symptoms are extremely common in children and adolescents, a population who often find it difficult to express their feelings and emotions through language. It is understood that 2–10% of children in the general population complain of bodily aches and pains (stomach aches, joint pains and headaches) that are likely to be medically unexplained (Garralda, 2005). Sometimes, these symptoms lead to significant distress, impairment in functioning and healthcare-seeking behaviour. Somatising disorders can have a significant impact not only on the children themselves but also on their families and healthcare resources. If somatising continues into adulthood it can lead to wide-ranging distress and impairment.

Developmental factors have an important influence on the presentation of disorders. One such factor is that children and adolescents are dependants, largely reliant on adults for significant aspects of ‘illness behaviour’ (Mechanic, 1962). Illness behaviour includes the way in which symptoms are responded to, and the extent to which medical consultation and lifestyle alterations are undertaken. Parents and carers have a powerful impact when they respond to (or ignore) children's physical complaints, attribute significance to (or give reassurance about) these complaints, facilitate (or otherwise) the children's use of healthcare facilities and involve them in (or withdraw them from) normal life activities.

Other developmental factors, especially the level of cognitive and verbal competence, have long been recognised as important determinants of the ability to express emotional distress directly by speech. In young children, a variety of primitive and regressive behaviours are commonly recognised as signalling emotional discomfort of various kinds.