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Hydatidosis usually is seen in lung and liver in human. Involvement of the breast by hydatic cyst is rare. A 26 years old woman referred to our clinic due to a palpable mass in her right breast. In ultrasonography a cystic lesion was seen. In mammography an opaque well defined lesion with a thin calcified margin was seen in her right inferomedial maxillary zone with 3 and 4 cm diameters without breast tissue destruction or microcalcification. Diagnosis of hydatic cyst was suggested and confined by pathology. Hydatic disease of the breast is rare. However, it might constitute a potentially serious differential diagnosis of a breast lump in areas endemic for this disease.