A meeting on "Cancer Chemoprevention and Cancer Treatment; role of vitamin D, 1alpha,25-(OH)(2)D(3) and deltanoids" was held on the NIH Congres, Bethesda in November 2004. The following conclusions were presented at the end of this symposium. Vitamin D deficiency and insufficiency are worldwide problems and are associated with several health problems including higher cancer prevalence. There is convincing evidence that the active vitamin D hormone, 1alpha,25(OH)(2)D(3), can decrease cell proliferation, modify cell apoptosis and control malignant cell growth. Therefore academia, public funding agencies and industry should urgently design appropriate studies to better define the causal relationship between vitamin D nutrition and cancer, define the optimal vitamin D nutrition based on accurate 25(OH)D measurement and inform the public and medical profession accordingly. Selective vitamin D receptor modulators are a potentially interesting new class of chemopreventive and chemotherapeutic agents as demonstrated by several first generation analogs have provided a convincing proof of concept. In the mean time, the public should be informed about the risks of vitamin D deficiency and insufficiency and appropriate steps should be taken to improve the vitamin D nutritional status of large parts of the world population.