We report an all electron density functional study of three candidate structures for the B24N24 cage. The structures considered are an octahedral O round cage, S-4 symmetric cage that satisfies the isolated square rule, and a cage of S-8 symmetry with caps of (4,4) nanotube. The S-4 and S-8 cages are energetically nearly degenerate and are favored over the O cage containing six extra octagons and squares. The infra-red and Raman spectra of the three clusters show notable differences providing thereby a way to identify and possibly synthesize the cages. The ionization potentials and static dipole polarizabilities are also reported. (C) 2004 Elsevier B.V. All rights reserved.