The purpose of this study is to assess populations in Thailand at high risk for HIV-1 infection for potential efficacy trials of candidate HIV vaccines to include:

1. assess incidence of HIV-1 and volunteer retention
2. describe early viral load and CD4 counts
3. assess participant willingness to participate in HIV vaccine efficacy trials and other HIV prevention trials
4. describe volunteer risk behavior

Prospective cohort study of HIV-negative participants who will receive voluntary counseling and testing (VCT) for HIV-antibody in conjunction with questionnaires on risk behavior, willingness to participate in HIV vaccine trials and other HIV prevention trials at 4 month intervals for a period of 1 year. This study will follow 1000 HIV-negative volunteers with an expected minimum of 15-20 incident HIV-infections based on a minimum incidence rate of 1.5/100 person-years. Weighted incidence estimates will be calculated with exact 95% confidence intervals.

Inclusion Criteria:

• Man or woman aged 18-50 years
• Willing to provide location or contact information and allow contact
• Thai citizenship as identified by Thai National Identification card
• Ability and willingness to provide consent
• Availability for follow-up for the planned study duration

Exclusion Criteria:

• Persons who have a history of a medical or psychiatric disorder, that in the judgment of the investigator(s), would interfere with or serve as a contraindication to adherence to the study protocol or ability to give informed consent
• Persons who are known to be HIV-positive

Population in Thailand who are seeking HIV counseling and testing at TRCARC