BACKGROUND: The exact relationship between hormonal activity and prostate cancer(PCa) has not yet been clearly defined. One of the key hormones associated with PCa is testosterone(T). However, both in vitro and in vivo studies have shown that under some conditions T is capable of either promoting PCa growth or death. This article proposes a theory which resolves this apparent paradox. MODEL: The Estradiol-Dihydrotestosterone(E-D) model introduced in this paper proposes that 17beta-estradiol(E2) is essential for initiating the growth of PCa cells through the formation of telomeres. It also proposes that T is responsible for increasing the expression of proteins which cause apoptosis, or programmed cell death, and that 5alpha-dihydrotestosterone(DHT) is essential for preventing this. In addition, it is known that some T is converted to both E2 and DHT, which means that depending on the conditions, T is capable of either promoting the growth of or the killing of PCa.