Abstract: Hydatid cysts are caused by the larval form of Echinococcus granulosus. Humans are accidental intermediate hosts of this organism. The liver and lung are the most commonly affected organs. Hydatid disease is endemic in countries where sheep breeding constitutes an important means of livelihood. Breast involvement is rare, accounting for only 0.27- 0.37% of the localizations. We report a case of primary hydatid disease of the breast in 41-year old woman in Maragheh city (west of Iran).