Studies in cancer prevention show a strong connection between dietary habits, lifestyle and risk of carcinoma. An inverse relationship between serum vitamin D levels and human tumor incidence has also been demonstrated. In this review the authors will address the pathogenesis of hormone-dependent prostate cancer and of colorectal cancer. While the latter is particularly affected by nutrition, its etiology may also be partly related to hormonal action, since women are 30% less likely to succumb to colorectal cancer than men. There is evidence that elevated dietary calcium, phytoestrogens and folate intake have a positive role in tumor prevention. The authors suggest that this beneficial action is due not only to intrinsic antimitotic proapoptotic activity, but also to maintenance of an efficient synthesis in prostate and colon cells of calcitriol, the active metabolite of vitamin D, since this hormone has profound antiproliferative, prodifferentiating and proapoptotic activity in both prostate and colon cancer.