We developed various factor models of the Childhood Anxiety Sensitivity Index [Silverman, W. K., Fleisig, W., Rabian, B. & Peterson, R. A. (1991). Childhood anxiety sensitivity index. Journal of Clinical Child Psychology, 20, 162-168] and tested the goodness of fit of the models in an independent sample. Of primary interest was to examine the question that characterized the factor analytic studies conducted on the adult version of the anxiety sensitivity index, i.e. the ASI [Reiss, S., Peterson, R. A., Gursky, D. M. & McNally, R. J. (1986). Anxiety sensitivity, anxiety frequency and the prediction of fearfulness. Behaviour Research and Therapy, 24, 1-8]: is anxiety sensitivity in children a unidimensional construct, an orthogonal multidimensional construct, or a hierarchical construct? Two independent samples (a clinic sample and a nonclinical sample) were used for development and replication of the factor models. The clinic sample consisted of 258 children (105 girls and 153 boys) who presented to a child anxiety disorders specialty clinic. The unselected, nonclinic sample consisted of 249 children (122 girls and 127 boys) enrolled in an elementary school. The results provided strong empirical support for a hierarchical multidimensional model with either three or four first-order factors. The two factors that emerged that appeared to be robust were Physical Concerns and Mental Incapacitation Concerns. What remains unresolved is whether Control of anxiety symptoms and Social Concerns are to be differentiated (as in the hierarchical model with four first-order factors) or not (as in the hierarchical model with three first-order factors). In addition to discussing this issue, the convergence of the present study's findings with past findings obtained with the ASI is discussed.