This work focuses on the response of orthotropic sandwich composite plates with large deflections due to high lateral loads. The results have special application to the design of ship structures. A geometrical nonlinear theory is outlined, on the basis of the classical sandwich plate theory expanded by the higher-order terms in the strain displacement relations, including shear deformation. By use of the principle of minimum potential energy, two different analytical solutions are derived for the simply supported and the clamped cases. The solutions are presented as simple design formulae. The results of the analytical calculations are discussed and compared with numerical non-linear finite difference calculations and large-deflection experiments of equivalent plates. The presented methods lead to good results for plate response and provide the engineer with an alternative method for the design of sandwich plates subjected to high lateral loading. (C) 1997 Published by Elsevier Science Ltd. All rights reserved.