Previous ab initio studies of the (X) over tilde (2)A＇H2PO radical have reported dramatically differing P-O bond distances when using spin-restricted wave functions predicting two artifactual isomers of H2PO : a singly bonded oxygen-centered radical and a doubly bonded phosphorus-centered radical. We show that large basis sets coupled with high levels of dynamical electron correlation are required to correctly describe the P-O bond in H2PO as well as the unpaired electron density as evidenced by the Fermi contact terms and anisotropic components of the P-31, H-1 and O-17 hyperfine splitting (hfs) constants. The optimized geometry, harmonic vibrational frequencies, and hfs constants of H2PO were determined at several coupled-cluster levels of theory using both spin-restricted (ROHF) and spin-unrestricted (UHF) Hartree-Fock reference wave functions. The geometrical parameters at the coupled-cluster level with single, double, and perturbatively applied triple substitutions [CCSD(T)] using Dunning＇s correlation consistent polarized valence quadruple-zeta basis set (cc-pVQZ) are r(P-O)=1.492 Angstrom; r(P-H)=1.410 Angstrom; angle(HPH)=102.63 degrees; angle(HPO)=114.92 degrees. These are in excellent agreement with those derived from recent gas phase microwave data, with the surprising exception of the P-H distance which deviates 0.02 Angstrom from experiment. The value of the P-O harmonic stretching frequency at the CCSD(T) level within the cc-pVQZ basis set is 1190 cm(-1), in good agreement with the experimental fundamental frequency of 1147 cm(-1) obtained by Withnall and Andrews and in constrast to previous speculation that this experimental band may have been misassigned. Hyperfine splitting constants determined at the TZ2P(f,d)/UHF-CCSD(T) level are in very good agreement with experimental values with an average deviation of 23 MHz.