The enthalpies of combustion of alpha-, beta-, gamma- and delta-1,2,3,4,5,6-hexachlorocyclohexane (HCCH) isomers and of chlorocyclohexane (CCH), and the enthalpy of vaporization of CCH have been determined by precision combustion and vaporization calorimetry; the enthalpies of formation of these compounds are derived. These results are more reliable than values reported in the literature. The non-bonding interactions in these molecules are discussed using the group scheme, the electrostatic bond energy model and force field calculations.