Background: Hydatid cyst is a zoonotic infection caused by Echinococcosis granulosus. Primary single-intramuscular hydatid disease is rare, even in endemic regions of the world. Here we report the case of exceptional thigh mass due to a hydatid cyst in an Iranian man. Case presentation: An 86-year-old man, initially presented to Velayat teaching hospital surgery clinic in May 2017 with a single right-thigh mass, but physical examinations of other organs were unremarkable. Based on sonographic findings, the differential diagnosis was hydatid cyst. He underwent surgical resection of the cyst. Histopathological results confirmed the diagnosis. There was no evidence of recurrence of the lesion during the 23-month follow-up. Conclusion: Increase thigh mass due to a hydatid cyst is a rare event. In endemic regions with the presence of hydatid cysts, especially physicians of surgical clinics have to consider differential diagnosis of hydatid cysts in unusual locations in case of such a lesion.