Geometry, vibrational and NMR spectra of the icosahedral aza-closo-dodecaborane MeNB11H11 are calculated by ab initio methods. The results are compared with experimental data. They are in accord with local C5v symmetry of the cluster unit and local C3v symmetry of the methyl group. The boron atoms B7–B11 are coupled to B12 by the small constant 1J (11B, 11B) = 12 Hz.