The review evaluates the role of vitamin D in carcinogenesis. Based on ecological studies, the incidence of many cancers has been shown to be higher in northern countries, suggesting an association with latitude and solar radiation. Vitamin D produced in skin under the influence of sun exposure may play a protective role in the process leading to cancer. Vitamin D deficiency is now recognized as a pandemic, mainly due to lack of knowledge that sun exposure in moderation is the major source of vitamin D for most humans. After vitamin D was discovered to be the necessary element of nourishment to prevent rickets at the beginning of the twentieth century, the theory concerning its role has evolved. It is now recognized that vitamin D, and particularly its active form 1.25 (OH)2D, is an important hormone playing a crucial role in human homeostasis. 1.25(OH)2D3 has been shown to inhibit cancer cell growth, induce cancer cell maturation, induce apoptosis, and decrease angiogenesis. Several studies suggested that living at higher geographical latitudes increased the risk of developing and dying of colon, prostate, breast and other cancers. People exposed to sunlight were noted to less likely develop cancer. Several studies evaluated circulating levels of 25(OH)D and its possible association with cancer. Case-control studies and laboratory tests have consistently demonstrated that vitamin D plays an important role in the prevention of breast cancer. Vitamin D supplementation is a much needed, low cost, effective, and safe intervention strategy for breast cancer prevention that should be implemented. It has been shown that vitamin D levels are lower in ovarian cancer patients. Low 25(OH) D concentration associated with lower overall survival rate might suggest for the important role of severe deficiency in more aggressive course of ovarian cancer. Testing for 25(OH)D in the standard procedure could help to find ovarian cancer patients with worse prognosis, who would benefit from special attention and supplementation. Vitamin D3 supplementation in moderate doses achieving 25(OH)D concentrations of 30-80ng/ml, can be recommended as many benefits may be expected, including decreased risk of developing cancer.