HIV infected adolescents may have a significantly higher capacity for immune reconstitution following highly active antiretroviral therapy (HAART), compared to adults. Despite this advantage, HIV infected adolescents are often reluctant to get proper medical care, follow through with doctor appointments, and adhere to medication schedules and regimens necessary to keep their infection under control. Lopinavir/ritonavir (LPV/r), a PI, and efavirenz (EFV), a non-nucleoside reverse transcriptase inhibitor (NNRTI), both have long half-lives that make them ideal drugs for the adolescent population, as they are more forgiving if patients miss or sleep through doses. The availability of once-daily dosing of LPV/r will reduce pill burden and offers more flexibility in medication scheduling, also helping to promote treatment adherence among this age group. This study will examine the effectiveness of two HAART regimens, one with the PI LPV/r and two nucleoside reverse transcriptase inhibitors (NRTIs), and the other with the NNRTI EFV and two NRTIs. The efficacy of therapeutic drug monitoring (TDM) and subsequent dose adjustment will also be assessed with both regimens.