Lattice constants and magnetic moments of face-centered cubic ( fcc) and body-centered cubic ( bcc) phases of cobalt obtained from self-consistent spin-polarized total-energy calculations by the augmented spherical wave method are compared to measurements. The calculated lattice constants fit the measured values of both phases to about 1%, but favor one of the two reported results on the newly-synthesized bcc phase. However the reported magnetic moments are substantially lower than the theoretical value for the bcc phase. We show that bcc cobalt is metastable up to 400 kbars pressure and, like fcc cobalt, is a strong ferromagnet. The magnetic moment of fcc cobalt is shown to collapse at a 5% lattice compression.