We report a reparameterization of the glycosidic torsion χ of the Cornell et al. AMBER force field for RNA, χ_OL. The parameters remove destabilization of the anti region found in the ff99 force field and thus prevent formation of spurious ladder-like structural distortions in RNA simulations. They also improve the description of the syn region and the syn–anti balance as well as enhance MD simulations of various RNA structures. Although χ_OL can be combined with both ff99 and ff99bsc0, we recommend the latter. We do not recommend using χ_OL for B-DNA because it does not improve upon ff99bsc0 for canonical structures. However, it might be useful in simulations of DNA molecules containing syn nucleotides. Our parametrization is based on high-level QM calculations and differs from conventional parametrization approaches in that it incorporates some previously neglected solvation-related effects (which appear to be essential for obtaining correct anti/high-anti balance). Our χ_OL force field is compared with several previous glycosidic torsion parametrizations.