As postulated by Fowler and Ugalde [J. Phys. Chem. A 2000, 104, 397], the lowest-energy B-13(+) isomer proved to be highly aromatic. The topological resonance energy of this cationic boron cluster is positive in sign and very large in magnitude. This constitutes the definitive reason B-13(+) is kinetically stable and planar or quasiplanar in geometry. The electron-deficient and multivalent character of boron is responsible for the high aromaticity of this cluster. In addition, its minimum bond resonance energy is not too small.