 Based upon the above study, the goal of the present cohort study is to examine prospectively in an expanded population of children who attend the PIDC the relationship between the HIV subtype infecting Ugandan children and their virologic and clinical response to the ARVs now available to this population. Approximately 30 of children are currently failing based primarily upon clinical data ARV therapy at the PIDC. In this study, these children will have a separate tube of 5 cc of blood drawn at specified times for HIV subtyping to examine whether specific subtypes of HIV are associated with failure to specific ARVs or ARV combinations. In addition to HIV subtype determination, viral genotyping viral mutations will be performed to examine the relationship between the HIV subtype and specific viral mutations indicating resistance to an ARV. 