Tested the utility of assessing anxiety sensitivity in children by investigating the incremental validity of the Childhood Anxiety Sensitivity Index (CASI) in a sample of clinic-referred children and adolescents ages 6 to 17 (N = 280). In the first test we examined whether the CASI would predict variance in trait anxiety beyond that predicted by measures of manifest anxiety and fear in children ages 6 to 11 (n = 202) and adolescents ages 12 to 17 (n = 78). In the next test, we examined whether the CASI would predict variance in fear beyond that predicted by a measure of trait anxiety for both age groups. In addition, age was tested as a continuous moderator of the CASI's incremental validity. No evidence was found to suggest that age systematically influences the CASI's incremental validity in the age ranges for which the CASI was designed. We discuss the results in terms of the utility of the CASI with younger and older age groups of children and the importance of such a measure for investigating the development of anxiety disorders in children.