Accurate diagnosis and assessment of anxiety disorders in children and adolescents is important for both treatment and research. In this paper, we review research related to the discriminant validity of the childhood anxiety disorders, and outline methods of assessment for children, including diagnostic interviews, self-report instruments, and behavioural, cognitive, and psychophysiological measures. Particular attention is given to psychometric and developmental issues, and their influence on assessment. The evidence provides support for the validity of the anxiety disorders as a whole, but only partial support for differentiation between specific anxiety disorders in children. Similarly, assessment methods used with anxious children provide reasonably accurate information on anxious symptoms, however are limited by poor discriminant validity and lack of sensitivity to developmental levels.