Children in this study will include patients who are HIV infected, were exposed to HIV or anti-HIV drugs prior to or at the time of their birth, or children of patients followed at Pediatric AIDS Clinical Trial Group (PACTG) sites. Children will have a study visit every 3 months through the first year of life. After age 1, children who are HIV infected will continue to have study visits every 3 months, while children who are HIV uninfected will have study visits once a year. Study assessments will include complete physical exam, medical history, Tanner staging, neurologic exam, growth and quality of life assessments, and laboratory tests such as hematology, chemistries, and urinalysis. Not all assessments will be performed at each study visit. Patients will be followed until age 24.