It is explicitly shown, that calculated sum over all states of the nonlinear optical properties (NLO) of molecular system (polarizability, hyperpolarizability, etc.) is exactly zero when wave functions which satisfy the Hellmann-Feynman theorem is used. These sum rules are correct for sum over energy levels (i.e., translation, rotation, oscillation and electronic) in case of any one-electron properties which can be described by the Hamiltonian H-0 + lambdaH((1)), where H-0 is the Hamiltonian of the unperturbed molecule and lambda and H-(1) represent external perturbation and the one-electron operator of any physical property, respectively. (C) 2004 Elsevier B.V. All rights reserved.