The microwave spectra,of 1,2- and 1,7-dicarba-closo-dodecaborane-(12), C2B10H12(ortho- and meta-carborane), have been recorded for the first time at room temperature in the 32-88 and 24-80 GHz spectral ranges, respectively. The spectra of the parent species (1,2-(C2B10H12)-B-11 and 1,7-(C2B10H12)-B-11) have been assigned, together with those of four monosubstituted (B-10) 1,2-(C2BB9H12)-B-10-B-11 and 1,7-(C2BB9H12)-B-10-B-11 isotopologues. The microwave spectra confirm that the structures of each of these two molecules are slightly distorted icosahedrons of C-2v symmetry. A previous determination of the gaseous structures of these two carboranes by the gas electron-diffraction method was based on several assumptions about the B-B bond length differences. All B-B bond lengths have now been redetermined using the substitution (r(s)) method, which is independent of such restraints. Although several of the r(s) and electron-diffraction bona lengths are In good agreement, there are also differences of up to 0.026 angstrom. Quantum chemical calculations at the B3LYP/6-311++G(3df,3pd) level of theory have also,been performed.