Here we report a case of co-infection of hydatid cyst with invasive apergillosis, in a previously healthy, non immunocompromised, 26year old man. Chest x-ray revealed a large cystic cavity in left upper lobe of lung histopathologic examination of the specimen confirmed the diagnosis of hydatid cyst with numerous fungal hyphea which invaded the laminated wall of the cyst. Although, co-infection with hydatid cyst is very rare finding but, in this patient hydatid cyst caused a new cavity formation which is the most common predisposing factor for development of aspergilloma, so we should consider aspergillosis infection in every lung cavity formatio
