We report the first case of constrictive pericarditis in a woman with systemic lupus erythematosus (SLE). Immunopathologic studies demonstrated IgG, IgA, IgM and C3 distributed throughout her pericardium including vessel walls. Cardiospecific antimyosin, antisarcolemmal and antipericardial antibodies were detected in serum obtained prior to surgery or steroid therapy. Antibodies disappeared and creatine phosphokinase decreased to normal concentrations during prednisone therapy. Antimyosin antibodies were not detected in 11 sera or in one pericardial fluid obtained from patients with lupus with active pericarditis unaccompanied by constriction. Evaluation of antimyosin antibodies in other patients with this rare manifestation of SLE is warranted to further assess their pathologic significance.