Equations governing the coupled thickness‐shear and flexural vibrations of isotropic, elastic plates are solved for the case of a circular disk with free edges. The results of computations are given for the resonant frequencies analogous to those which would be excited in an AT‐cut quartz disk with full electrode coating. A marked difference is observed between the frequency spectrum of the disk and the spectrum of cylindrical vibrations of a rectangular plate. The difference is due to the presence of thickness‐twist modes of motion, in the disk, which, along with the thickness‐shear modes, are coupled to the flexural modes.