Detailed ab initio electronic structure calculations are reported for octahedral and prismatic isomers of CrF6. A carefully graded series of basis sets has been used. Correlation effects were calculated at the CCSD(T) level, and some exploratory MR-CISD calculations were performed. Vibrational frequencies calculated at the SCF level are reported. In agreement with other recent work, the octahedral isomer is shown to be the most stable for CrF6; the crucial role played by f functions in the Cr basis is emphasized. Triple excitations preferentially stabilize the octahedral isomer. Our final value for the octahedral-prismatic energy electronic energy separation is 59.3 kJ/mol, which is much lower than the CASPT2 result reported by Pierloot and Roos (Inorg. Chem. 1992, 31, 5353).