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.

Inclusion Criteria:

Groups 1 and 2 (If co-enrolling in ATN 061)

• HIV positive participants age 18 years and 0 days to 24 years and 364 days (the lower age limit of this study is driven by the restriction of ATZ use to age 18 and greater);
• Groups 1 and 2: CD4+ T cells above 350 cells/mm3 and HIV RNA >1,000 copies/ml, as determined by two consecutive measures within 6 months of entry with the second measure being collected at pre-entry to ATN 061;
• Infected with HIV after the age of nine via behavioral means;
• Naïve to ART except for HAART for PMTCT for six months or less with at least six months since the time of exposure;
• HIV genotype without major resistance mutations to the recommended ATV-r based HAART regimens;
• Able to provide written informed consent as determined by local Institutional Review Boards;
• Fluent in English or Spanish.

Group 2, enrolled in ATN 071 and not ATN 061

• CD4+ T cells above 350 cells/mm3 and HIV RNA >1,000 copies/ml, as determined by most recent laboratory evaluations available within 4 months prior to entry;
• Not prescribed HAART according to DHHS guidelines.

Groups 3 and 4:

• HIV positive participants age 18 years and 0 days to 24 years and 364 days;
• Infected with HIV after the of age nine via behavioral means;
• Naïve to ART except for HAART for PMTCT for six months or less with at least six months since the time of exposure;
• Able to provide written informed consent as determined by local Institutional Review Boards;
• Fluent in English or Spanish.
• CD4+ T cells < 350 cells/mm3, as determined by most recent laboratory evaluations available within 4 months prior to entry.

Group 3 ONLY:

• Participant initiating HAART.

Group 4 ONLY:

• HAART has not been prescribed due to either participant's refusal to initiate HAART or provider's concerns about participant's predicted inability to adhere to regimen.

Exclusion Criteria:

Groups 1 and 2:

• For Groups 1 and 2: any history of an AIDS-defining illness;
• Active drug or alcohol use or dependence that, in the opinion of the site personnel, would interfere with meeting study requirements;
• History of cognitive or motor impairment due to non-HIV-related conditions (for example, prematurity, cerebral palsy, closed head injury, CNS cancer or cranial irradiation, etc.) or psychosis. Youth with diagnoses of learning disabilities or attention deficit hyperactivity disorder will be allowed in the study;
• Enrollment of youth with chronic or acute medical conditions other than HIV that could potentially impact upon neurocognitive functioning requires protocol chair approval.
• Pregnancy at any time during the study including entry.

English or Spanish speaking youth, 18 years 0 days to 24 years 364 days, with HIV-1 infection acquired after age 9 via behavioral means, in the following immunological and treatment categories:

1. Early initiation of HAART and enrolled in 061 Arm A; CD4+ T cells above 350 cells/mm3 and HIV RNA >1,000 copies/ml;
2. Initiation of HAART per DHHS guidelines (standard of care) but not yet meeting criteria. There will be 25 participants from ATN 061 preferentially enrolled into this protocol; an additional 25 participants will be enrolled with similar biomedical characteristics.
3. Initiation of HAART per DHHS guidelines (not part of ATN 061).
4. Meeting DHHS guidelines for initiating HAART, but not initiating due to unwillingness or providers' expectation of poor adherence.