The Scaled Particle Theory (SPT) is probably the most powerful theory presently available, that enables the calculation of the thermodynamic functions relative to the formation of cavities in liquids. We give the general relationship between the enthalpy of vaporization and the enthalpy of formation of a molecular cavity in a pure normal liquid; the good agreement with the experimental data constitutes one of the strongest arguments justifying the application of SPT to real liquids. However, we show that SPT can lead to uncertain cavity terms if the molecular diameters of the studied liquids are not well-known. We compare, on the other hand, the cavity terms (GandH) calculated from Sinanoglu's theory, since this theory has been used to that end recently, with those obtained from SPT.