A total of 60 participants will be enrolled. They will be in 3 groups

1. ARV-naïve, HIV-positive ≥ 20 year of age with HAD (n=20) who intend to start ARV
2. ARV-naïve, HIV-positive ≥ 20 year of age without HAD (n=20), who intend to start ARV
3. HIV-negative ≥ 20 year of age (n=20). The protocol team will work with the primary care physician to ensure that the subjects receive standard HIV and ARV care; however, initiation of ARV is not a requirement of the study and ARV will not be provided by the study.

Inclusion Criteria:

1. Thai HAD individuals

   • 20 years of age

     • not currently receiving nor have ever received antiretroviral medications
     • not explained by opportunistic infections or causes other than HIV on the basis of clinical assesssment and neuropsychological testing and eligible for inclusion.

2. Thai Non-HAD individuals

   • will be matched with a seropositive Thai patient with similar age (same decade), education (less than high school degree, high school degree +/- some college, college degree +), gender, and CD4 group
   • HIV positive
   • not currently receiving nor have ever received antiretroviral medications.
3. Thai Non-HAD individuals will be matched with a Thai seronegative patient by age (same decade), and education (less than high school degree, high school degree +/- some college, college degree+), and gender.

Exclution Criteria:

1. Head injury with loss of consciousness greater than 1 hour
2. Current or past illicit drug use (less then 5 years) or positive drug screen for amphetamine, methamphetamines, cocaine, marijuana, or narcotics at either screening or entry.
3. Inability to provide informed consent or lack of designated surrogate who can provide consent

4. The following laboratory values:

   • PT/PTT > the upper limit of normal (ULN) or INR > 1.1
   • Hemoglobin < 9.0 mg/dL
   • ALT > 5x ULN
   • serum creatinine > 2x ULN or creatinine clearance < 30 cc per min by Cockroft-Gault formula
5. Acute illness within 30 days prior to entry, persistent and active AIDS- defining opportunistic infection or autoimmune disease. Stable treated opportunistic infections on maintenance therapy, minor infections such as oral thrush and Kaposi's Sarcoma limited to the skin will be allowed.
6. Current or recent fevers or meningeal signs suggestive of CNS opportunistic infection.*
7. History of pre-existing neurologic disease to include stroke, multiple sclerosis
8. History of psychiatric illness including schizophrenia, bipolar disorder, anxiety disorder, panic attacks, or post traumatic stress disorder. Patients with active major depression will be excluded as well - patients with past depresion that is controled and patients with or minor depressive symptoms will be allowed to enroll.
9. Known learning disability including dyslexia.
10. Positive Hepatitis C serology (Hepatitic C Ab)
11. Confusion or other signs and symtoms of metabolic encephalopathy or delirium
12. Mass consistent with opportunistic infection or tumor on CT or MRI of the head, or focal neurological deficit on examination consistent with possible brain lesion.*
13. Other conditions that could explain neurocognitive decline in the opinion of the investigator such as hypothyroidism, vitamin B12 deficiency or neurosyphilis.
14. Pregnancy.
15. Not willing to take an MRI.