The role of vitamin D in the immune system is complex. Vitamin D is produced in the skin following exposure to ultraviolet radiation. There is compelling evidence that vitamin D compounds protect against ultraviolet radiation-induced DNA damage and immune suppression, suggesting it may be beneficial as a skin cancer preventive agent. However, vitamin D has many modulatory effects on the immune system and it has in fact been suggested that the immune suppression generally attributed to the UVB portion of sunlight is mediated through vitamin D. Here we describe the role of vitamin D compounds as "defence" molecules against UVR-induced damage, and investigate both sides of the "fence" regarding the effects of vitamin D compounds and the immune system.