A numerical method for the analysis of elastic thin-walled box girders is presented. The method is based on the separation of variables suggested by Vlasov and on the finite element method. The method is capable of taking into account longitudinal and transversal flexure, torsion, distortion of the cross section, torsional and distortional warping and shear deformation. Stresses and displacements calculated with the computer program developed for a straight one-box girder have been compared with results obtained by other analytical and numerical methods and with experimental data.