We report the rare case of a multicystic mesothelial cyst of the mediastinum. A 43-year-old man was referred to our department after a routine chest X-ray showed an anterior mediastinum mass. The lesion was resected by thoracoscopy, which revealed multicystic, thin-walled tense masses arising in the anterior mediastinum. The cysts were not adherent to the pericardium or to the thymus of the right lobe. Immunohistochemistry revealed that the cyst was lined with a layer of mesothelial cells and there were no malignant foci. The lining cells were positive for keratin and negative for the lymphocyte marker. These findings were consistent with a diagnosis of multicystic mesothelial cyst.