An 86-year-old man with a serum prostate-specific antigen level of 93.33 ng/ml was diagnosed as having cT3aN0M0 prostatic adenocarcinoma of Gleason score 9. Although the serum prostate-specific antigen responded well to combined androgen blockade, the cancer spread and lead to death 6 months after diagnosis. The patient had leukocytosis during the clinical course with no sign of localized infection, especially after manipulation of the prostate. Enzyme immunoassay demonstrated elevated serum levels of granulocyte colony-stimulating factor (G-CSF) and macrophage colony-stimulating factor. To our knowledge, this is the first case of prostate cancer with G-CSF production, which was confirmed immunohistochemically.