As new drugs and vaccines are developed to prevent HIV disease progression and prolong survival of HIV infected patients, the short-term safety and effectiveness of these treatments are evaluated in research studies. However, the long-term effects, whether they are benefits or side effects, need to be studied as well. These long-term effects may have a greater impact on infants and children who are still growing and developing. The purpose of this study is to follow HIV-exposed and HIV infected infants, children, and adolescents who are seen at Pediatric AIDS Clinical Trials Group (PACTG) study sites. These patients will be observed for long-term benefits or any late harmful effects of medications or vaccines.