The miscibility of poly(vinyl chloride) (PVC) and an ethylene-vinyl acetate copolymer with 85 wt% of vinyl acetate units (EVA85) has been studied by measuring the glass transition temperature and the enthalpy of mixing of several mixtures covering the whole composition range. An accurate thermal characterization as regards the specific heat of the two polymers and their blends has also been obtained. The enthalpy of mixing has been found negative for all the mixtures, indicating that specific interactions are involved between the polar groups of the two components. Particular attention has been paid also to the excess specific heat, which comes out positive for the PVC-rich blends and with a small negative value in a narrow region at high contents of EVA85. This finding is in agreement with negative and positive deviations that are observed for the glass transition temperature. Modelistic considerations about the type of interactions and the organization between PVC and EVA85 in the blends are proposed.