Semiempirical MNDO and Density Functional Theory (DFT) are applied to investigate the structure and properties of Cn-2BN fullerenes, where n = 20, 24, 28, 32, 36, and 40. Low-mass fullerenes are of particular interest because of their high curvature and increased strain energy owing to adjacent pentagonal rings. The most important factor for stability is the connectedness of the heteroatoms. The BN group prefers to replace a short CC bond. N atoms tend toward smaller angles, leading them toward participation in pentagons over hexagons. The BN pair prefers hexagon−pentagon over pentagon−pentagon junctions. No systematic trends are observed in the effects of doping upon the HOMO-LUMO gap, ionization potential, and electron affinity. Whereas MNDO is unable to reliably predict the most stable isomers, single-point DFT calculations at MNDO-optimized geometries correctly reproduce the full DFT relative energy trends.