Self-consistent field ab initio calculations have been performed for CH3Br. The calculated equilibrium conformation is in good agreement with experiment. Valence and core level ionization potentials, Mulliken population analysis and electronic properties are presented. The ionization potentials are in good agreement with the experimental values, except for one case in which the experimental value may be wrongly assigned. The calculated dipole moment, 2.43 Debye, is 34% or 0.6 Debye larger than the experimental value. © 1977 Springer-Verlag.