The breast is a rare primary site of hydatid disease and accounts for only 0.27% of cases. Mammary hydatidosis generally occurs in females and has never been described in male patients. In this paper, the authors report a new case of isolated hydatid cyst of the breast in a 35-year-old previously healthy man, who presented with a left breast painless lump of one year duration. Physical examination showed a non-tender and immobile mass in the upper lateral quadrant of the left breast, with normal overlying skin and nipple. There was no palpable lymph node in the left axilla and the contralateral breast was normal. Ultrasonography showed a 2.7 x 1.5 cm cystic lesion in the left breast. The patient underwent total excision of the mass, and histopathological examination confirmed the diagnosis of hydatid cyst. The authors conclude that although hydatid cyst of the breast is rare, it should be considered in the differential diagnosis of breast lumps especially in endemic areas.