Advancements in anti-HIV drugs for HIV infected children and adolescents have been hard to make, in part because these patients often do not take the drugs as prescribed. ATV may be a better option because it is available in the form of powder which children and adolescents may be more willing to take regularly. Using a low dose of RTV as a boosting agent for ATV may also increase the chances of virologic response of highly active antiretroviral treatment (HAART)-experienced patients. This study aimed to find safe and tolerable doses of ATV with or without low-dose RTV boost in infants, children, and adolescents. For this study, participants were enrolled in the United States and South Africa.