BACKGROUND: Use of antiretroviral therapy (ART) to prevent HIV transmission has received substantial attention after a recent trial demonstrating efficacy of ART to reduce HIV transmission in HIV-discordant couples. OBJECTIVE: To assess practices and attitudes of HIV clinicians regarding early initiation of ART for treatment and prevention of HIV at sites participating in the HIV Prevention Trials Network 065 study. DESIGN: Cross-sectional internet-based survey. METHODS: : ART-prescribing clinicians (n = 165 physicians, nurse practitioners, physician assistants) at 38 HIV care sites in Bronx, NY, and Washington, DC, completed a brief anonymous Internet survey, before any participation in the HIV Prevention Trials Network 065 study. Analyses included associations between clinician characteristics and willingness to prescribe ART for prevention. RESULTS: : Almost all respondents (95%), of whom 59% were female, 66% white, and 77% HIV specialists, "strongly agreed/agreed" that early ART can decrease HIV transmission. Fifty-six percent currently recommend ART initiation for HIV-infected patients with CD4+ count <500 cells per cubic millimeter, and 14% indicated that they initiate ART irrespective of CD4+ count. Most (75%) indicated that they would consider initiating ART earlier than otherwise indicated for patients in HIV-discordant sexual partnerships, and 40% would do so if a patient was having unprotected sex with a partner of unknown HIV status. There were no significant differences by age, gender, or clinician type in likelihood of initiating ART for reasons including HIV transmission prevention to sexual partners. CONCLUSIONS: This sample of US clinicians indicated support for early ART initiation to prevent HIV transmission, especially for situations where such transmission would be more likely to occur.