A 60-year-old male was transported to our hospital by ambulance because of dyspnea. On admission, he exhibited left pleural effusion and multiple masses in the left thoracic wall and was subsequently diagnosed with malignant pleural mesothelioma. Enhanced chest computed tomographic scans showed rapid growth of the masses within a single week. One cycle of chemotherapy with carboplatin and pemetrexed was administered; however, the masses continued to increase in size, and the patient died 39 days after admission. During the administration of chemotherapy, 75 μg of G-CSF was administered from the 8th to 11th days of treatment after the development of grade 2 neutropenia, and the patient's white blood cell count persistently increased to 47,900/μl before his death. Upon pathological dissection, the malignant mesothelioma lesion was suspected to be a G-CSF-producing tumor. Cells from this kind of tumor are thought to have receptors for G-CSF, allowing the lesions to grow independently. Therefore the G-CSF tumor possibly caused the rapid tumor growth observed in this case.