Three hundred and eighty nine preoperative localizations were performed in the senology department of the Centre Jean Perrin in 349 patients presenting with an isolated radiological image with no associated clinical signs (discovered on routine or selective screening examinations). The most frequent anomaly detected was the presence of areas of microcalcifications, sometimes associated with a high-density lesion or more rarely an opacity. Systematic enlargements allowed refinement of the surgical indications and reduced the number of tumourectomies performed for benign lesions. The histological results consisted of 41% of neoplastic and borderline lesions with a predominance of in situ or microinvasive forms without lymph node involvement. The mean age at the time of diagnosis was 40 years, i.e. ten years younger that the mean age of cancer diagnosis. The percentage of subclinical cancers discovered in this way, increased by screening and improvement in surgical techniques, has been further increased by enlargements which have improved the precision of surgical indications. Stereotactic localization allows the surgeon and pathologist to more accurately define the lesion while preserving the appearance of the breast.