Pericardial cysts frequently are recognized when they present in a cardiophrenic angle, but may not be suspected when they occur elsewhere in the chest. To highlight the unusual presentations of pericardial cysts, we present two patients with cysts in the upper mediastinum and review the reported experience with similar lesions. Our patients' cysts are particularly instructive because one cyst enlarged over 23 months and because the other did not appear cystic on a computerized tomographic scan. Because percutaneous aspiration may be an attractive alternative to surgical resection when a pericardial cyst is suspected, clinicians should include pericardial cyst in the differential diagnosis of upper mediastinal masses.