Due to the increasing occurrence of and high costs associated with prostate cancer (PC), there is an urgent need to develop novel PC treatment and chemoprevention strategies. Although androgen receptor (AR) signaling is significant in the development and progression of PC, other molecular pathways contribute as well. Peroxisome Proliferator-Activated Receptor Gamma (PPARγ) has recently been implicated as an oncogene in PC, which may influence both the development and metastatic progression of the cancer. There are two isoforms of PPARγ, with PPARγ2 having an additional 30 amino acids at the amino terminus. Here, we investigated the differential expression and function of these two isoforms in benign and cancerous prostate epithelial cells. The findings from our immunohistochemistry (IHC) and RNA in situ hybridization experiments suggest that although both isoforms are expressed in benign human prostate tissue, PPARγ1 predominates in PC tissue. Our results from PC cell line experiments suggest that PPARγ1 contributes to the proliferation of some PC cells and that PPARγ2 represses PC cell growth. Our findings also suggest that PPARγ1 increases the growth and possibly the transformation of otherwise benign prostate epithelial cells. These results help to establish different roles for PPARγ isoforms in prostate cells, and support the hypothesis that PPARγ1 acts as an oncogene and that PPARγ2 acts as a tumor suppressor in prostate cells.