Every organ can be involved by hydatid disease. Liver and lung are the most common sites but muscles, due to high level of lactic acid and contractility, are among the rare areas involved by hydatid cysts. In 2009, a 23 year old Zanjanian villager girl came to clinic because of having a mass at her right thigh from 3 years ago. Present and past medical history, blood count and serologic evaluation was negative for hydatosis, but MRI, diagnosis during the operation and eventually pathologic evaluation confirmed the diagnosis of hydatid cyst. Hydatid disease should be considered in differential diagnosis of masses, involving the limbs, especially at endemic areas in order to prevent rupture of the cyst during operation which can cause anaphilaxis and involvement of other tissues.