A new simplified approach is presented for calculating the flexural frequencies of a composite-material plate undergoing moderately large, normal deflections. The plate may be arbitrarily laminated with respect to the midplane, so that bending-stretching coupling is present. The approach used is a generalization of the work of Wah for homogeneous, isotropic plates. In the case of orthotropic plates, it differs from various orthotropic extensions of the popular Berger hypothesis. The present theory is applied to the practical case of a clamped rectangular plate with finite in-plane restraint. The results are compared satisfactorily with those of previous analyses for various special cases.