The crystal structure of cobalt vanadophosphate dihydrate {systematic name: poly[diaqua-mu-oxido-mu-phosphato-hemicobalt(II)vanadium(II)]}, Co(0.50)VOPO(4).2H2O, shows a three-dimensional framework assembled from VO5 square pyramids, PO4 tetrahedra and Co[O2(H2O)4] octahedra. The Co(II) ions have local 4/m symmetry, with the equatorial water molecules in the mirror plane, while the V and apical O atom of the vanadyl group are located on the fourfold rotation axis and the P atoms reside on 4 sites. The PO4 tetrahedra connect the VO5 polyhedra to form a planar P-V-O layer. The [Co(H2O)4]2+ cations link adjacent P-V-O layers via vanadyl O atoms to generate an unprecedented three-dimensional open framework. Powder diffraction measurements reveal that the framework collapses on removal of the water molecules.