In a cirrhotic patient, an increase in intra-abdominal pressure due to the presence of ascites might lead to a small pleuroperitoneal bleb of the peritoneum from congenital defects in the hemithorax. This lesion may appear as an intrathoracic mass as seen on a simple chest radiograph. A CT image may be helpful to differentiate an ascitic pleuroperitoneal bleb from an intrathoracic mass. We present three cases of a pleuroperitoneal bleb in patients with liver cirrhosis and ascites.