ATN 071 is a prospective cohort study comparing neurocognitive functioning in four groups of youth, age 18-24: Two groups with CD4+ T cells above 350 cells/mm3 and HIV RNA >1,000 copies/ml, one initiating HAART (Group 1) and the other not initiating treatment (Group 2); and two groups with CD4+ T cells < 350 cells/mm3, one initiating treatment (Group 3) and the other not initiating treatment (Group 4). Groups 2 and 3 represent standard of care. Group 1 and a portion of group 2 will be co-enrolled in ATN 061 and will be randomly assigned to group by that protocol.