This is a comprehensive observational study of HIV infection in homosexual and bisexual men.

The Multicenter AIDS Cohort Study (MACS) provides important information about the changing nature of HIV-mediated disease progression, the impact of antiretroviral treatment, the nature of HIV pathogenesis, and viral and host genetic factors. This study will also assess the long-term patterns of therapy use and risk-taking behaviors.

Patients will have study visits every 6 months. The visits will include interviews, specimen collection, and a physical examination.

Inclusion Criteria:

• HIV negative, or
• HIV positive and no history or current use of highly active antiretroviral therapy (HAART), or
• HIV positive HAART recipient with documentation of HAART initiation, no AIDS diagnosis prior to HAART initiation, and a CD4 cell count and HIV-1 RNA measurement within 6 months prior to first HAART use.
• Sexual intercourse with men or at least 5 male or female partners in the 5 years prior to enrollment.

Exclusion Criteria:

• Injection drug use within 1 year of enrollment.
• Perinatally acquired HIV infection.

Homosexual and bisexual men with and without HIV infection