A 54-year-old male patient presented with a granulocyte colony-stimulating factor (G-CSF)-producing primary pericardial mesothelioma, while showing symptoms of congestive heart failure, a fever of 38 to 39 degrees C, and marked leucocytosis of 52.7 x 10(3) cells/mm3. The histopathologic diagnosis was established after autopsy. G-CSF production was confirmed by the expression of G-CSF mRNA in the tumor extract and the patient's high serum G-CSF concentration. The expression of G-CSF by benign and malignant mesothelial cells has already been reported. However, this is the first case report of G-CSF production in a pericardial mesothelioma.