Peroxisome proliferator-activated receptor (PPAR) is a member of the nuclear hormone receptor superfamily of transcription factors. Peroxisome proliferator-activated receptor gamma (PPARgamma) plays an important role in the regulation of lipid homeostasis, adipogenesis, insulin resistance, and development of various organs. Agonists of PPARgamma have been also reported to inhibit proliferation of prostate carcinoma cells as in other human malignancies, and these synthetic ligands have been used in differentiation-mediated therapy of various human carcinomas associated with high levels of PPARgamma. The significance of PPARgamma expression, however, was unknown in human prostate carcinoma tissues. The purpose of the present study was therefore to examine the immunolocalization of PPARgamma in human prostate cancer tissues (40 cases) and correlate the findings with clinicopathological features of the patients in order to evaluate its possible biological significance. Twenty-nine patients were positive for PPARgamma immunoreactivity (73%) and a significant inverse correlation was detected between PPARgamma immunoreactivity, pT stage (P = 0.036), and serum concentration of prostate-specific antigen (P = 0.0004). In conclusion, PPARgamma immunoreactivity is considered to be a new clinicopathological parameter of human prostate cancer.