To assess the prevalence and risk factors of neurocognitive impairment and psychiatric comorbidities in HIV infected patients who have undetectable viral load, have been on HAART for at least 1 year and have no history of CNS infection.

To understand how to prevent and treat HIV-associated neurocognitive impairment and psychiatric comorbidities in HIV-infected Thai individuals who don't have current AIDS related illness or current and prior central nervous system (CNS) infection, and have been well treated with HAART with undetectable HIV RNA.

Inclusion Criteria:

• Signed informed consent
• Evidence of HIV infection (confirmed positive ELISA and documented history of measurable HIV RNA)
• Age > 18 years old
• Plasma HIV RNA of < 50 copies/ml within 3 months prior to screening
• Have been on only NNRTI-based HAART regimen for the entire duration and for at least1 year.

Exclusion Criteria:

• Current AIDS defining illnesses
• Current or history of previous CNS infection.
• Head injury with loss of consciousness greater than 1 hour
• Acute illness within 30 days prior to entry that, in the opinion of investigators, would prevent patients from completing the protocol required procedures.
• Known learning disability including dyslexia

HIV infected adults with viral < 50 copies/ml on NNRTI based HAART