The nonframework cation sites for K-ETS-10 and Na-ETS-10 have been modeled using molecular simulation techniques. This work combines a Monte Carlo packing procedure with lattice energy calculations, to simulate the charge-balancing cation sites in a titanosilicate, starting from only the framework structural data. One hundred trial packing arrangements for each cation type were randomly generated with the Monte Carlo procedure, and the lattice energy for each of these structures was calculated, considering electrostatic and repulsive short-range terms, For both K+ and Na+ cations, most of the initial arrangements converged to an identical minimum energy structure, involving four different cation sites, The relative stability of these sites depends on their framework environment and the kind of cation that occupies them.