The purpose of this work is describing a mass classification method as part of a CADx scheme in mammography, specifically based on comparisons between densities of the breast tissue and the mass under investigation itself.The technique is designed to be simple and fast, allowing it to be used simultaneously to the image overview, once the specialist has selected a suspected region to the analysis. Tests so far used the DDSM database that contains an overlay marking the approximate contour of the detected masses.