There is growing evidence that vitamin D exerts anticarcinogenic effects. Ultraviolet-B (UV-B) radiation, which is required for vitamin D production in the skin, was found to be inversely associated with cancer incidence and mortality. Recent studies have largely but not consistently shown that low 25-hydroxyvitamin D (25(OH)D) levels, which are considered to be the best indicator of vitamin D status, are a significant risk factor for cancer mortality. Circulating 25(OH)D levels were also associated with improved survival in colorectal and lung cancer patients and vitamin D insufficiency was observed in various other diseases such as autoimmune, infectious, musculoskeletal, neurological and cardiovascular diseases. In conclusion, we still need further studies to evaluate the association of vitamin D insufficiency and cancer incidence and mortality, but the multiple health benefits of vitamin D and the easy, safe and inexpensive way by which vitamin D can be supplemented should already guide current public health strategies to achieve 25(OH)D levels of at least 75 nmol/l (30 ng/ml) in the general population.