A 19-year-old man was admitted with a history and examination findings of probable bacterial pericarditis. Blood cultures produced Neisseria meningitidis Group C, sensitive to penicillin. The patient was initially treated with intravenous benzylpenicillin. Echocardiogram demonstrated the development of a pericardial effusion which was tapped, and benzylpenicillin was instilled into the pericardial space. Because of failure of clinical resolution, cefotaxime was substituted for benzylpenicillin. Rapid clinical improvement then ensued. Repeat echocardiogram showed evidence of neither reaccumulation nor constrictive pericarditis. Primary (isolated) meningococcal pericarditis is a recognized though rare manifestation of meningococcal disease. It is most common in young adults and is associated with a good prognosis.