The rarity of mammary echinococcosis leads the authors to report the demonstrative case of a 45-year-old woman, para 9, gravida 9, who had always breast fed, undergoing surgery for a cyst of the right breast and which was found histologically to be a hydatid cyst. Progression of the tumour was particularly slow (approximately 10 years). Mammography forms an essential part of pre-treatment evaluation since it enables circumscription of the lesions and study of regional lymph nodes which are normal in all cases. At any event, cystectomy is the only effective method of treatment, recognised by all authors. Clinical and mammographic evaluation after 2 years of our patient was normal.