A formulation is given for the large-deflection behaviour of eccentrically stiffened steel plates. Plasticity, in both the plates and stiffeners, is treated using approximate yield criteria that are direct functions of the stress resultants and plastic curvatures. The formulation has been successfully tested against alternative experimental and theoretical solutions for beams and columns. The scope of the method is illustrated by examples relating to concentrically stiffened box girder diaphragms and eccentrically stiffened compression panels