Pleuropericardial cysts are unusual congenital presentations of mediastinal tumors which shares its origin with pericardial diverticulum .Caused by the failure of fusion of one of the mesenchymal lacunae that form the pericardial sac .These are unilocular , well marginated or spherical structures that are attached to the pericardium or diaphragm by a pedicle . Histologically these cysts are lined by mesothelial cells , the wall composed of collagen and elastic fibres with chronic inflammation. We present a case of a 42 year old man with chronic cough. A routine chest x–Ray showed a near complete collapse of his left lung due to a large mass .