We describe a patient with an infected right atrial thrombus and pulmonary embolism who died suddenly. Jejunal diverticulitis, which was found at autopsy, was suspected to be the source of the bacterial thrombus. The 41-year-old female patient was admitted because of dyspnea and syncopal attacks. Physical examination on admission revealed an obese woman with a body temperature of 36.5 degrees C, systolic heart murmur and abnormal diastolic heart sound. Two-dimensional echocardiography revealed a strand-shaped mass in the right atrium. Lung blood perfusion scintigraphy revealed multiple perfusion defects in both lung fields. She suddenly developed severe dyspnea leading to death on the 6th hospital day. At autopsy, a strand-shaped organized thrombus was found in the right cardiac chambers. Microscopically, the thrombus was found to be infiltrated with numerous gram-positive cocci, leukocytes and a small number of gram-negative cocci. Most of the major pulmonary arterial branches were occluded by bacterial thromboemboli, and multiple pulmonary infarctions were found in both lungs. A perforating diverticulum with microabscess was found in the jejunal mucosa which was assumed to be the source of the bacterial thromboembolism.