The investigators propose a two-phase study to establish safety and efficacy of high dose vit D supplementation in children and adults with HIV/AIDS. In Study Phase I, the safety and efficacy of two oral vit D3 doses (4000 and 7000 IU/d) are determined over 12 weeks in 44 subjects ages 5.0 to 24.9 y. The key safety measure is concurrently elevated serum calcium and 25D concentrations. Efficacy is evaluated by serum 25D concentration and cathelicidin (innate immune, antimicrobial protein) mRNA expression. Study Phase II is a 12 month, double blind, randomized, placebo controlled supplementation study (n=52). Key outcomes include safety and longterm 25D concentration within the goal range (32 to 160 ng/mL), improved cathelicidin mRNA expression, and measures of bone, muscle, inflammation, growth and body composition status, and HIV/AIDS disease severity. Based on the evidence and promise, vit D clearly deserves to be among the first nutrients evaluated in the National Center for Complimentary and Alternative Medicine (NCCAM) HIV research program.