Optimized geometries and total energies of a series of aza[60]fullerenes, C-60-N-2n(2n), have been calculated by density functional theory using B3LYP/6-31G*. The minimum total energy of C58N2 is the isomer with a pair of N atoms sitting in the (1,4) positions of the [60]fullerene. Maximum relative stability in the series is obtained for the isomer of C48N12 with one N per pentagon and S-6 point group symmetry. The nitrogen content in C48N12 is in close agreement with the observed nitrogen concentration in fullerene-like onions of CNx. C48N12 is iso-electronic with C-60(-12) and has an ionization potential which is 1.6 eV lower than that of C-60.