The case history of an 18-yr-old asymptomatic woman with primary chylous pericardium is reported. On the basis of this case and those reported in the literature, it is suggested that the diagnosis should be established by echocardiograms, cardiac angiograms, and pericardiocentesis. Lymphangiograms are useful for the detection of the underlying abnormality of the lymph vessels. Pericardiectomy together with thoracic duct ligation are the preferred treatment. Generalized lymphatic abnormality is probably the underlying mechanism of this entity. This lymphatic abnormality could be associated with impaired cellular immunity, although no such impairment was found in this patient.