The authors describe a case of squamous cell carcinoma of the esophagus that was initially diagnosed as hydropneumopericardium at radiography. The patient subsequently underwent computed tomography (CT) and esophagography. CT revealed pneumopericardium, pericardial thickening, a mass in the esophagus, and bilateral effusion. Esophagography demonstrated perforation of the mid-thoracic esophagus and marked irregularity of the esophageal mucosa. To the authors' knowledge, this is the only reported instance of esophageal carcinoma initially diagnosed as hydropneumopericardium. CT can be used as a primary method to investigate spontaneous pneumopericardium.