BACKGROUND: We present a case of a hydatid cyst located in the left thigh.CASE REPORT: A 67-year-old man was admitted to our department with a 10 × 5 × 4 cm mass in the medial compartment of the left thigh. Computed tomography scan indicated possible hydatidosis. Serological testing (indirect hemagglutination) was positive for hydatidosis. The patient was operated seven years ago for liver hydatidosis.RESULTS: The patient, after evaluation, underwent surgical excision of the cyst under epidural anesthesia. The cyst was located in the left quadriceps muscle; had a soft, elastic substance; was firmly attached to the muscle fibers; and contained transparent fluid and daughter cysts. Histologic examination confirmed the initial diagnosis. The patient was discharged on the fifth postoperative day.CONCLUSIONS: The diagnosis of muscular hydatidosis is difficult and the usual diagnostic methods are the serological tests for hydatidosis and imaging (e.g., ultrasound, computed tomography, and magnetic resonance imaging). In every soft tissue mass with benign characteristics the existence of a hydatid cyst should always be considered. Careful surgical excision of the intact cyst is the treatment of choice, but complementary control for liver-or other organ-hydatidosis should be performed.