Advancements in HAART for HIV-infected children and adolescents are hindered by patient nonadherence. The availability of a powder formulation and the once-daily dosing schedule make ATV an attractive agent for improved adherence in pediatric treatment regimens. This study was designed to provide pharmacokinetic (PK) data to guide dosing recommendations for ATV, when given concurrently with or without low-dose RTV boost, in infants, children, and adolescents. During the study, the safety and tolerance of ATV (with or without low-dose RTV) were closely monitored, and virologic efficacy data were obtained.