Evaluation of the lateral-torsional buckling resistance of bisymmetrical I-section beams using finite element method was widely discussed in the paper. Numerous FEM simulations with regard to the stability behavior of steel structural elements subjected to bending about the major principal axis were performed. The use of different finite element modeling techniques and their influence on obtained results were presented by the authors. The ultimate state of both perfect and imperfect elements was assessed. Considerations were concerned with hot-rolled wide flange HEB and narrow flange IPE section beams. Idealization of boundary conditions of FEM models complies with the assumptions used in the analytical formulation of stability problems of thin-walled beams. Geometrically and materially nonlinear analyses GMNA and GMNIA preceded by LBA analyses were carried out. Numerical simulations were conducted with use of ABAQUS/ Standard program.