In 1997, a 53-year-old male smoker was admitted for progressive shortness of breath associated with a productive cough and yellowish sputum, pleuritic chest pain, and low-grade fever. There was no history of trauma. A posterior-anterior chest radiograph showed a diffuse infiltrate through the right lung field and an air space parallel to the lateral border of the heart. A computed tomographic scan of the chest confirmed pneumopericardium, with no associated pericardial effusion. It also showed a cavitary infiltrate in the anterior basal segment of the right lower lobe, but no definite neoplasm. Cultures of the sputum grew Staphylococcus aureus. The patient had positive antibodies to human immunodeficiency virus (HIV), hepatitis A, and hepatitis B. A bronchial biopsy from the right lower lobe showed well differentiated infiltrating squamous cell carcinoma with an acute inflammatory exudate. No bronchopericardial fistula was noted. After antibiotic treatment, a repeat chest radiograph showed resolution of pneumopericardium and improvement of the chest infiltrate. Repeat computed tomography of the chest showed that the pneumopericardium had resolved, but now revealed a large pericardial effusion. No bronchopericardial fistula could be demonstrated. Unfortunately, our patient refused further investigation. Pneumopericardium is a rare disorder. In adults, pneumopericardium most commonly results from trauma. Although many other reports link pneumopericardium to an underlying disease process, our patient with HIV antibodies developed pneumopericardium despite having no history of trauma and no documentation of a communicating fistula. To our knowledge, there has been no previous report of pneumopericardium in association with acquired immunodeficiency syndrome.