Cardiobacterium hominis is a Gram-negative coccobacillus, which is part of the normal human oropharyngeal flora. C. hominis is recognized as a rare cause of human infection leading to endocarditis and focal infections outside the vascular system. To our knowledge, there is no reported case of C. hominis pericarditis without endocarditis. A 10-year-old girl was admitted to our hospital with the complaints of fever, sweating, palpitations and chest pain lasting for 1-week. Her physical examination revealed a body temperature of 39 8C, decreased breath sounds in the left lower lobe of the lung and decreased heart sounds. Blood pressure was 90/60 mmHg and pulse was 88/min. There was no pulsus paradoxus. The liver edge was 2 cm palpable. Other systems’ examination were normal. Laboratory analysis revealed white blood cell count: 10 000/mm, antistreptolysin O: 415 IU/ ml, CRP .201 mg/dl and erythrocyte sedimentation rate: 92 mm/h. There was marked enlargement of the cardiac silhouette on telecardiogram. Echocardiographic examination demonstrated massive pericardial effusion. There were no findings of echocardiographic pericardial tamponade. Left ventricular diameters and ejection fraction were also normal. There were no valvular dysfunction and no demonstrable vegetation in any of the heart valves on transthoracic and transesophageal echocardiography. Computed tomography of the thorax showed pericardial effusion and left sided pleural effusion, therefore 1000 cc of serous pericardial fluid was drained by partial pericardiectomy and 250 cc of serous pleural fluid was drained by thoracentesis. Histopathologically, the surgical specimen revealed purulent exudative membranes. Pleural and pericardial fluids were cultured. Before identification of the etiologic agent, broad spectrum antibiotic was started empirically (vancomycin 40 mg/kg/day parenterally and cefotaxime 150/ mg/day parenterally) against the most common micro-organisms possibly causing, bacterial pericarditis. Although the pleural fluid and blood cultures were negative, culture of the pericardial fluid revealed C. hominis. Once culture and susceptibility testing were available antibiotic therapy was continued with cefotaxim alone for two more weeks. At the end of 4 weeks of antibiotic treatment, all laboratory measurements were in the normal range and there was no pericardial fluid collection on echocardiographic examination. Pericardial and pleural fluid were incubated on trypticase soy agar with 5% sheep blood, chocolate agar, Eosin methylene blue agar (EMB) and Sabouraud agar at 35 8C in an atmosphere of 5% carbon dioxide. On the 3rd day of incubation partially Journal of Infection (2005) 50, 346–347