Density functional theory has been used to investigate gas-phase thermodynamic properties of phenol and dichlorophenols. Molecular geometries, energies, and vibrational frequencies were computed at the B3LYP and BP86 levels of theory. At T = 298.15 K, calculated standard enthalpies of formation are in excellent agreement with experimental data. The average deviation between calculated and experimental values is of about 2.3 kJ/mol, and in some cases, theoretical values fall within experimental uncertainty. Other proper-ties for which only a few experimental results were available in the literature were also calculated, namely, O-H homolytic bond dissociation energies, gas-phase acidities, ionization energies, and proton and electron affinities.