Antiretroviral therapy in children aims to prolong clinical and immunologic health. Currently, there are no data defining a particular highly active antiretroviral therapy (HAART) strategy as the optimal first-line therapy for children. This study evaluated the long-term efficacy of two HAART regimens used as initial therapy: 1) two nucleoside reverse transcriptase inhibitors (NRTIs) plus a protease inhibitor (PI), and 2) two NRTIs plus a nonnucleoside reverse transcriptase inhibitor (NNRTI). It also evaluated different strategies for switching therapy when the initial regimen fails. The long-term nature of this study should clarify whether early switching of therapy improves immunologic and virologic outcomes, or results in a more rapid exhaustion of treatment options. The study was conducted in the United States and in Europe.