The vibration behavior of rectangular laminated composite plates subject to in-plane loading is investigated employing a global higher-order theory. The displacement field is expanded in the thickness direction in a complete polynomial series with arbitrary degree whereas the series coefficients, function of the in-plane coordinates, are expressed, according to Ritz's method, as a superposition of admissible functions. The elastic and geometric stiffness matrices as well as the mass matrix are obtained from the energy functionals in terms of the generalized coordinates. The problem is suitably nondimensionalized so as to single out the independent parameters. Variations of the lowest frequencies with the width-to-thickness ratio and with the ratio between the in-plane elastic moduli are investigated to ascertain the sensitivity of the vibration behavior with respect to these parameters. Effects of the lamination scheme on the vibration properties are assessed.