In the current chapter, we use the term fear to label the brain state elicited by a threat, a stimulus for which an organism will extend effort to avoid. We use the term anxiety to label a brain state that is highly similar to fear but that occurs in the absence of a threatening stimulus. While these definitions derive from research in experimental psychology and neuroscience, they apply equally well to clinical phenomena. Fear and anxiety represent normal reactions to danger; both exhibit well documented age-related fluctuations with strong crosscultural similarity. These fluctuations typically begin with increases in stranger and separation anxiety in toddlers, followed by fears of physical harm in early school-age years. Anxiety about competence, abstract threats, and social situations typically increases during adolescence. Relatively brief periods of anxiety related to these issues represent a normal aspect of human development (8,9). As a result, major questions arise concerning boundaries between “normal,” or developmentally appropriate, and abnormal expressions of anxiety, as manifest in anxiety disorders.

One critical differentiation between normal fears or anxiety and an anxiety disorder derives from the so-called impairment criterion: To receive an anxiety disorder diagnosis there must be significant impairment or interference in the child’s everyday functioning. Behavioral avoidance is a primary area of impairment that might lead children to avoid many typical experiences enjoyed by peers. Anxiety or fear is also considered abnormal when the level of distress evoked by danger is considered extreme, relative to a child’s peers. However, this “distress” criterion typically has been more difficult to apply than the “impairment” criterion. Such difficulty arises from the fact that fewer guidelines are available for determining when “distress,” relative to “impairment,” appears “clinically significant.”

Definitive data on prevalence and demographics of common syndromes derive from epidemiological studies randomly selecting subjects from the community. Available data suggest that 2.8%–27% of children and adolescents might be afflicted with some form of pediatric anxiety disorder, broadly conceptualized (10). Rates vary based on the definition used, assessment methods, specific disorders considered, and age ranges of the subjects. In terms of demographic correlates, the strongest findings document an excess of anxiety in females relative to males. This gender difference is found both in studies that rely on self-report scales and in studies that rely on diagnostic interviews for virtually all anxiety diagnoses (6,11). Interestingly, female preponderance in anxiety emerges before puberty, which is earlier than in depression, which typically first manifests in females at puberty. An exception to this rule may be found in GAD, which appears to follow a pattern similar to depression, becoming more common in girls during adolescence (12,13).

Some demographic data document distinctions among the anxiety disorders. For example, SAD has an earlier age of onset than the other anxiety disorders (14), and it shows dramatic reductions in prevalence with age. Social phobia, in contrast, typically exhibits an increase in prevalence during adolescence, which is consistent with normative developmental trajectories (6,15).