When lesions cannot be clearly identified by sonography or mammography and if their images are clinically occult, their cytology or histology confirmation is required. Stereotactic biopsy allows an accurate locating of non palpable lesions, that are also invisible at sonography. The choice between a fine needle aspiration biopsy and core needle micro-biopsy depends upon local and technical possibilities but above all upon mammographic aspect of the lesion. When microcalcifications have to be identified both methods should be used.