Using the density functional method, the stabilities of highly hydrogenated and fluorinated [80]fullerenes, both empty and containing the SC3N molecule, have been calculated. Addition of 44 atoms to i-SC3NCso is predicted to be most favorable due to the formation of six octahedrally located benzenoid rings, while addition of up to 52 atorns (consistent with preliminary fluorination data) gives a structure stabilized by the presence of four benzenoid rings. The most stable isomers at this addition level have been determined and the relative stabilities of a number of C80H52, C80F52, and i-SC3NC80H52 species calculated. The hydrogenation of the i-SC3NC80 has been computed to be more difficult than the corresponding partner, C-80. From the geometrical point of view, the SC3N molecule is planar in the parent [80]fullerene but is calculated to be pyramidal in some of the hydrogenated/fluorinated derivatives. Moreover, in these it has fixed locations due to orbital interactions arising from deformation of the cage and the presence of localized double bonds.