It has been more than 100 years when it was first appreciated that increased sun exposure reduced risk of dying of cancer. The most beneficial effect of sun exposure is the production of vitamin D in the skin. Recent evidence suggests that most cells in the body not only have a vitamin D receptor but also have the capacity to convert 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D. Once formed 1,25-dihydroxyvitamin D can inhibit cellular proliferation, induce cellular maturation, inhibit angiogenesis and ultimately cause apoptosis to prevent malignancy. A multitude of studies have associated improved vitamin D status with decreased risk for developing several deadly cancers including colon, breast, pancreatic and ovarian cancers. Patients with cancer are at high risk for vitamin D deficiency. Sensible sun exposure, vitamin D fortification and vitamin D supplementation should be encouraged to improve the vitamin D status of children and adults not only for bone health but for reducing risk of developing and dying of cancer. The goal is to achieve a blood level of 25-hydroxyvitamin D of 40-60 ng/mL. This can be accomplished by children taking 600-1000 and adults 1500-2000 international units (IU) vitamin D daily from diet and supplements along with sensible sun exposure when the sun is capable of producing vitamin D in the skin.