Vitamin D's role in bone health has been well established. Recently, studies have identified additional roles of vitamin D in the immune system, cardiovascular system, and cancer prevention. The effect of vitamin D on the immune system is particularly relevant to the dermatologist in that it has implications for atopic dermatitis, psoriasis, and skin cancer. However, there is much disagreement on a dose of vitamin D that is both safe and effective as both ultraviolet exposure and certain vitamin D-rich foods come with unwanted consequences. This review aims to update the dermatologist on the roles of vitamin D in the immune system, the safety and dose of different sources, and risk factors for vitamin D deficiency that may necessitate supplementation. Immune consequences of vitamin D status represent one additional aspect that illustrates how guidelines for supplementation are needed and will only be useful clinically if they are presented in context with validated controlled clinical trials.