A finite element model for elastic-plastic analysis is presented. The formulation is based on a minimum principle requiring the optimization of a functional with respect to the independent fields of displacements and plastic multipliers. Connections with traditional procedure are explored. Some deficiencies of the formulation, due to the independent modelling of the two distributions of variables, are also discussed and some consistency criteria able to overcome the above shortcomings are proposed. Simple examples illustrate the proposed procedure, which can be expected to be efficient and reliable.