Endocrine disrupting compounds may interfere with tissues at critical developmental stages and give rise to cancer later in life. This talk will focus on early-life exposure to endocrine disrupting chemicals which is associated with increased risk for carcinogenesis in mammary and prostate glands in experimental models. On the other hand, some naturally occurring endocrine disruptors (phyto-estrogens) have been proposed as protective against mammary cancer. Our recent rat studies showed an increased prevalence of intraductal hyperplasia of mammary glands after perinatal exposure to estrogenic chemicals, and this was associated with early changes in pre-pubertal mammary development. In the prostate, we observed a shift from the general age-related atrophy towards hyperplasia in aging rats that had been exposed perinatally to a mixture of human relevant anti-androgenic chemicals. This causes concern that human perinatal exposure to environmental chemicals may increase the risk of prostate or mammary cancer later in life. Possible modes of action and the human relevance of these findings will be discussed.