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The brominated flame retardants (BFRs), 1,2-dibromo-4-(1,2 dibromoethyl)cyclohexane (TBECH) and 2,3-dibromopropyl-2,4,6-tribromophenyl ether (DPTE) bind to the androgen receptor (AR). in vitro bioassays have shown that TBECH is a potent androgen agonist while DPTE is a potent AR antagonist. Both TBECH and DPTE alter gene expression associated with AR regulation. However, it remains to be determined if TBECH and DPTE can affect the prostate. For this reason, we exposed CD1 mice to a 1:1 mixture of TBECH diastereomers α and β, a 1:1 mixture of γ and δ, and to DPTE, and tested their effects on prostate growth, histology and gene expression profiles. Castrated mice were used to study the androgenic effects of TBECHαβ and TBECHγδ while the antagonistic effects of DPTE were studied in non-castrated mice. We observed that testosterone and TBECHγδ increased body and prostate weights while TBECHαβ affected neither of them; and that DPTE had no effect on body weight but reduced prostate weight drastically. Histomorphometric analysis of the prostate revealed epithelial and glandular alterations in the TBECHγδ group comparable to those in testosterone group while alterations in the TBECHαβ group were less pronounced. DPTE displayed androgen antagonist activity reminiscent of castration. The transcription profile of the prostate was altered by castration and exposure to testosterone and to TBECHγδ reversed several of these changes. Testosterone and TBECHγδ also regulated the expression of several androgen responsive genes implicated in prostate growth and cancer. While DPTE resulted in a drastic reduction in prostate weight, it only affected a small number of genes. The results indicate that TBECHγδ and DPTE are of high human health concern as they may contribute to changes in prostate growth, histology and function.