A 69-year-old man was admitted to our hospital because of anorexia and weight loss. Abdominal computed tomography showed an irregularly contoured mass in his left renal pelvis. The patient had a remarkable degree of leukocytosis with no obvious focus of infection. An enzyme immunoassay of the serum revealed a remarkably high concentration of granulocyte colony-stimulating factor (G-CSF). The patient died 6 weeks after admission without a resection of the renal pelvic tumor. At autopsy, the tumor involved the pancreas, stomach, and descending colon. The histopathologic diagnosis was squamous cell carcinoma with sarcomatous change. Immunohistochemical staining using anti-G-CSF antibody demonstrated immunoreactivity in the cancer cells. To our knowledge, this is the first case of renal pelvic carcinoma proven to produce G-CSF reported in English.