ABSTRACT
This chapter provides a brief description of the major diagnostic systems and the most common disorders in children and adolescents, and their prevalence. Knowledge about the basis for categorizing disorders is important for clinicians to be able to recognize, understand and communicate the problems children can experience. Many disorders require the presence of only a certain number of the symptoms. Children who meet the criteria for a given disorder do not necessarily experience exactly the same problems or symptoms. As activity and participation are directly associated with functioning and disability, an individual's activities and participation are key elements in the characterization of disabilities. Disability is defined as a deviation from what is possible or common, related to impaired body function, restricted activity or limited participation. The child's age is taken into account in the coding of functions and deviations.
