We have observed that vitamin D deficiency, as evidenced by low serum 25(OH)D concentrations, is common in children and adolescents with HIV infection. To determine whether vitamin D and calcium supplementation improve bone mineral content (BMC) and bone mineral density (BMD) in HIV-infected children and adolescents, we propose a double-blind, randomized, placebo-controlled trial comparing supplementation with oral vitamin D and calcium to placebo.