A computational study of 2-phosphinylphenol has been carried out to investigate intramolecular hydrogen bond formation and its consequences in the rest of the molecule. This is an extension of both our synthetic work on organophosphorus derivatives of diphenyl ether and our experimental and computational structure analyses of salicylaldehyde, 2-nitrophenol, and related molecules. Full optimization of the 2-phosphinylphenol geometries was carried out both at the HF/6-31+G** level and, to include electron correlation, at the MP2/ 6-31G* level. The stabilization energy of the intramolecular hydrogen bonding in 2-phosphinylphenol (28.4 kJ/mol by isodesmic calculation) is smaller than that of the intermolecular hydrogen bonding in the dimer of 2-phosphinylphenol, also computed in this work to be 59.1 kJ/mol per hydrogen bond from the counterpoise interaction energy or 57.4 kJ/mol by BSSE-corrected isodesmic calculation. The closure of the six-membered ring with the intramolecular hydrogen bond apparently introduces energy-costing constraints. The geometrical changes in 2-phosphinylphenol accompanying the formation of the hydrogen bond are similar to those observed in 2-nitrophenol and salicylaldehyde, characterized as resonance-assisted hydrogen banding. In addition to the lowest energy monomer with the hydrogen bond, two further stable minima of higher energy with no hydrogen bonding were found for 2-phosphinylphenol.