The energy levels of the 5f(3) manifold of the free-ion U3+ Up to 30 000 cm(-1) are calculated with two well stabilized ab initio methods based on the two-component Hamiltonians of Cowan-Griffin-Wood-Boring and Douglas-Kroll-Hess. Although the corresponding experimental data do not exist, estimates made out of experiments on the 50 manifold of U3+ in solids are usually referred to as the experimental energies of U3+ in gas phase. On the basis of a discussion on the available data of f-element ions in gas phase and in solids and a discussion on the expected precision of the present calculations, we suggest that the 50 energy levels of free U3+ are higher than the estimates and lower than the present ab initio calculations. (c) 2006 Elsevier B.V. All rights reserved.