Density functional theory (DFT) methods have been used to predict the geometries and a variety of energetic quantities of fluorinated closo-monocarborane clusters. Geometries were optimized at the local DFT level and energetics obtained at the gradient-corrected level. The species studied were CB 11H 12 −, 2-, 7-, and 12-CB 11H 11F −, 7,8,9,10,11,12-CB 11H 6F 6 − (CB 11H 6F 6 −), 1-H-CB 11F 11 −, and fragments of the parent anion obtained by removing an H atom or an H − ion from a given cluster vertex. For the anions CB 11H 12 −, 12-CB 11H 11F −, CB 11H 6F 6 −, and 1-H-CB 11F 11 −, the optimized CB 11 cores were icosahedral cages with C 5 v symmetry. The predicted CB, BB, CH, BH, and BF bond distances are in good agreement with available experimental data and, in the case of CB 11H 12 −, with bond distances predicted at the MP2 or Hartree–Fock levels of theory. The calculations show that dissociation of H − from CB 11H 12 − or F − from CB 11H 11F − varies by more than 12 kcal mol −1 depending on which type of boron vertex is chosen (the dissociations are most endothermic for upper-belt BH and BF bonds). In contrast, the dissociation of H or F atoms varies by less than 2 kcal mol −1 for the three types of boron vertices. The calculations predict that 2-CB 11H 11F − is marginally more stable than 7-CB 11H 11F − or 12-CB 11H 11F − (the relative energies are 0, 0.91, and 0.17 kcal mol −1, respectively), despite the observation that 12-CB 11H 11F − is the only isomer formed when CB 11H 12 − is treated with liquid anhydrous HF. Therefore, the DFT results suggest that regioselective fluorination of CB 11H 12 − under the conditions that have been used is under kinetic control.