Ellipsometric formulae for thin films non-uniform in thickness are presented. A general type of thickness nonuniformity is considered and the influence of the varying angle of incidence is taken into account. The presented formulae are applied to the optical characterisation of polymer SiO(2)-like thin films exhibiting a relatively strong thickness non-uniformity. It is shown that the complete optical characterisation of these polymer thin films can be performed. Thus, the spectral dependences of the optical constants, mean thickness and parameters related to the shape of thickness non-uniformity can be determined. (C) 2010 Elsevier B.V. All rights reserved.