We have investigated the performance of seven popular density functionals (B3LYP, BLYP, BP86, mPW, OPBE, PBE, PW91) for describing the geometry and stability of the hydrogen bonds in DNA base pairs. For the gas-phase situation, the hydrogen-bond lengths and strengths in the DNA pairs have been compared to the best ab initio results available in the literature (MP2). For a comparison with the crystallographic experiments, the first crystal-environment shell was taken into account in our DNA model systems. BP86 and PW91 excellently recover both the ab initio and experimental values. B3LYP consistently underestimates hydrogen-bond strengths and overestimates hydrogen-bond distances. (c) 2006 Elsevier B.V. All rights reserved.