[Pulmonary leiomyosarcoma].

We present the case of a young patient with leiomysarcoma of the lung that was at first diagnosed as a hydatid cyst. Pathological tissue analysis was needed for firm diagnosis. This rare tumor, of which fewer than 100 cases have been reported worldwide in the literature, needs to be considered as a differential diagnosis when lung cancer is suspected, given that leiomysarcoma has a better prognosis. Treatment is mainly surgical.