An expression for the excess partial molar volume of electrolyte solutions was derived in the framework of the mean spherical approximation (MSA). This integral theory, an extension of the Debye-Huckel theory, includes the effect of the ion size in the radial ion-ion distribution function, and it allows the description of excess thermodynamic properties of electrolytes over a wide range of concentration. The general pressure and temperature dependence of the excess volume predicted by the model were analyzed for model electrolytes, and the results for NaCl aqueous solutions at temperatures up to 300 degrees C were compared with experimental data over a wide range of concentrations (up to 4 mol.kg(-1)). Crystallographic and adjustable ion diameters were used in the calculations, allowing reasonable predictions of the NaCl(aq) excess volume over different concentration regions. The effect of ion association, excluded volume, and reference system conversion were also analyzed.