The aim of this work is to apply a group-contribution cubic equation of state to vapor-liquid equilibria calculations of polymer-solvent mixtures. The model is based on a Redlich-Kwong-Soave equation of state with Huron-Vidal mixing rules where infinite-pressure activity coefficients are predicted by a UNIFAC-type model. An original procedure for estimating the equation-of-state parameters of the polymer is developed : experimental activity data of solvents in binary systems with the same polymer are used to fit parameter b (actually, b/MW) of the polymer, so that only one value of polymer density is needed to calculate parameter a at the temperature of interest. To show the potential of the proposed approach. a table of parameter b values is provided for sis polymers, and several examples are presented both for nearly athermal and for polar polymer solutions. The model is able to correlate equilibrium pressure and solvent activities of the data base with good accuracy. The proposed method is then applied to predict solvent activities of systems not included in the fitting procedure with satisfactory results in all cases.