Despite the advances that have been made in the treatment and prevention of human immunodeficiency virus (HIV) infection in the United States, the numbers of cases in adolescents and young adults has continued to rise. Based on reports of new cases, the profile of the disease in this age group has been one that has evolved over the years to be increasingly female, minority, and marked by sexual transmission as the most likely mode of transmission of the infection. Research involving this population has been hampered by the presumption that many HIV positive youth are not linked into care and that the infrastructure for in depth research into the unique problems of this group has not been well developed. The Adolescent Medicine HIV/AIDS Research Network (AMHARN) has been a national study of the pathogenesis of HIV infection in youth. It has succeeded in characterizing the medical and psychosocial challenges facing HIV infected youth, and more importantly has cataloged the biologic parameters of HIV infection in these youth and contrasted them with that of a control group of demographically and behaviorally similar uninfected controls. This critical information will be useful in informing the adolescent specific HIV /AIDS scientific agenda. This proposal seeks support for our program for HIV infected adolescents to participate in a cooperative agreement as a clinical site for the nationally proposed Adolescent Medicine Trials Network (ATN). This Network will conduct research, both independently and in collaboration with existing research networks, to advance knowledge on promising behavioral, microbicidal, prophylactic, therapeutic, and vaccine interventions to both prevent and treat HIV infection. Nationally, up to 1500 HIV infected adolescents and 2500 non-infected controls will be recruited followed with the intention of making available to them an array of possible studies in which they may participate. Our Adolescent Trials Unit (ATU) will recruit at least 75 infected and 125 uninfected control youth as part of this overall effort. So developed, the Network will serve as the critical infrastructure for advancing the domestic research agenda unique to this age group.