Between 1952 and 1991, 15 Mayo patients were found to have partial or complete absence of the pericardium at the time of a cardiovascular surgical procedure. One patient with complete absence of the left pericardium had symptoms possibly related to the pericardial abnormality. This 42-year-old man had severe insufficiency of the tricuspid valve attributable to chordal rupture of the anterior leaflet, possibly precipitated by complete displacement of the heart into the left pleural space. Excision of the ruptured chordae and plication of the anterior flail leaflet rendered a competent tricuspid valve. In two patients, a small defect in the pericardium was repaired. Three patients who underwent operation for complex congenital heart disease died: two early postoperatively and one late after a reoperation. In the other 12 patients, no early or late postoperative complications were encountered. Although rare and usually asymptomatic, complete and partial deficiency of the pericardium may lead to serious complications such as cardiac valvular insufficiency or incarceration of cardiac tissue.