This report documents a case of systemic lupus erythematosus in which the major presenting feature was pericarditis and in which the diagnosis was made after pericardiocentesis by the demonstration of typical LE cells in pericardial fluid stained with Wright's stain. Review of the literature indicates that pericarditis in lupus is more common than is generally suspected, and when it is the initial manifestation it is often misdiagnosed as "benign viral pericarditis".Screening for collagen disease should be a part of the work-up of any patient presenting with pericarditis, especially a woman. Occasionally lupus may be present even when the serologic tests have given negative results. Under such circumstances, or when the patient manifests an atypical or prolonged course, a diagnostic pericardiocentesis is in order, provided an effusion can be confirmed on scan. A search for LE cells should be included in the analysis of the aspirated fluid.