For the automatic detection and characterization of nodules in a tomographic image of an anatomical zone of a patient, the image is segmented for identifying therein a region of interest, and the segmented image is processed for identifying the nodule.During the processing step, an ellipsoid inscribed in the region of interest is modeled for deciding whether the image elements inscribed in this ellipsoid correspond to a nodule, and, for each zone of the region of interest extending beyond the ellipsoid, the image elements are identified which do not belong to the module according to mathematical morphologic criteria.