Estrogen-modulated transgenic mice, such as estrogen receptor-knockouts (alphaERKO and betaERKO), aromatase-knockout (ArKO) and aromatase-overexpressing (AROM+) mice, have contributed to our understanding of the roles of estrogens in male reproductive biology, including prostate growth and development. Varying pathological changes of the prostate have been described as being the result of aberrant actions of estrogen, both directly through the estrogen receptors or indirectly by altering the endocrine status of these mice. This article identifies the consequences of aberrant estrogen signaling on prostate growth and development. Further characterization and manipulation of these estrogen-modulated transgenic mice will lead to a more complete understanding of the hormonal regulation of the mammalian prostate gland.