Ultraviolet (UV) radiation is an established carcinogen that causes skin cancers and other cutaneous photodamage. Vitamin D is produced in the skin after UV exposure and may also be obtained from dietary and supplemental sources. The effect of recommendations for UV protection, as well as for very large vitamin D supplements, and possible adverse effects of both are explored. Current evidence supports the conclusion that protection from UV radiation reduces the incidence of skin cancers and photodamage, but generally does not compromise vitamin D status or lead to iatrogenic disease. Conversely, risks of maintaining very high vitamin D levels have not been adequately studied. Vitamin D obtained from diet and supplements is functionally identical to that produced after UV exposure, and is a more reliable and quantifiable source of the vitamin.