The mammalian target of rapamycin (mTOR) is a crucial effector in a complex signaling network commonly disrupted in cancer. mTOR exerts its multiple functions in the context of two different multi-protein complexes: mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2). Loss of the tumor suppressor PTEN (phosphatase and tensin homolog deleted from chromosome 10) can hyperactivate mTOR through AKT and represents one of the most frequent events in human prostate cancer. We show here that conditional inactivation of mTor in the adult mouse prostate is seemingly inconsequential for this postmitotic tissue. Conversely, inactivation of mTor leads to a marked suppression of Pten loss-induced tumor initiation and progression in the prostate. This suppression is more pronounced than that elicited by the sole pharmacological abrogation of mTORC1. Acute inactivation of mTor in vitro also highlights the differential requirement of mTor function in proliferating and transformed cells. Collectively, our data constitute a strong rationale for developing specific mTOR inhibitors targeting both mTORC1 and mTORC2 for the treatment of tumors triggered by PTEN deficiency and aberrant mTOR signaling.