The key role of vitamin D (vit D) in maintaining optimal bone health has long been recognized, but its role in modulating the innate immune response and inflammatory reaction has only recently come under active investigation. As such, vit D is an increasingly frequently chosen and prescribed high dose dietary supplement,because it is thought to improve immune and inflammatory status in healthy people of all ages, and in those with chronic diseases including HIV/AIDS. Vit D also has calciotrophic functions essential for bone health, and poor vit D status contributes to the osteopenia/osteoporosis associated with antiretroviral therapy (ART). Vit D may improve insulin/glucose/lipid metabolism, blood pressure and risk of some cancers, all of which may complicate HIV/AIDS and its treatments. Poor vit D status is common in patients with HIV/AIDS of all ages and factors such as age, skin pigment, lactose intolerance and sun exposure alter the risks for vit D deficiency. In the multicenter U.S. REACH study of adolescents (72% African American), with and without HIV, showed that 87% had low serum 25D concentrations (<15 ng/mL), compared to 34% in a recent sample of healthy African American children from Philadelphia. Young African Americans are disproportionately affected by HIV infection in the US (~ 55% among persons with HIV aged 13 to 24 years are African American), and are also at high risk for vit D deficiency. Vit D therapy has great promise to improve major medical conditions and the quality of life for our patients with HIV/AIDS, yet the potential role of vit D in the treatment of HIV/AIDS has not been formally tested. Well-designed randomized trials are urgently needed to determine vit D supplementation safety and efficacy.