HIV-infected children, youth, and adults have lower bone mineral density (BMD) than would be expected for HIV-uninfected people of similar age, weight and race. As the majority of perinatally HIV-infected U.S. children are entering or in adolescence, the potential for HIV-related impaired BMD during the adolescent peak of bone mass acquisition is of particular concern. The primary purpose of this study was to compare changes from pre-treatment levels of BMD of the lumbar spine after 24 and 48 weeks of alendronate treatment with placebo in HIV-infected children and adolescents.