These guidelines replace CDC's 1994 guidelines, HIV Counseling, Testing, and Referral Standards and Guidelines, and contain recommendations for public- and private-sector policy makers and service providers of human immunodeficiency virus (HIV) counseling, testing, and referral (CTR). To develop these guidelines, CDC used an evidence-based approach advocated by the U.S. Preventive Services Task Force and public health practice guidelines. The recommendations are based on evidence from all available scientific sources; where evidence is lacking, opinion of "best practices" by specialists in the field has been used. This revision was prompted by scientific and programmatic advances in HIV CTR, as well as advances in prevention and the treatment and care of HIV-infected persons. These advances include a) demonstrated efficacy of HIV prevention counseling models aimed at behavioral risk reduction; b) effective treatments for HIV infection and opportunistic infections; c) effective treatment regimens for preventing perinatal transmission; and d) new test technologies. Although the new guidelines include many aspects of the previous ones (e.g., encouragement of confidential and anonymous voluntary HIV testing, need for informed consent, and provision of HIV prevention counseling that focuses on the client's own risk), the new guidelines differ in several respects, including: giving guidance to all providers of voluntary HIV CTR in the public and private sectors; using an evidence-based approach to provide specific recommendations for CTR; underscoring the importance of early knowledge of HIV status and making testing more accessible and available; acknowledging providers' need for flexibility in implementing the guidelines, given their particular client base, setting HIV prevalence level, and available resources; recommending that CTR be targeted efficiently through risk screening and other strategies; and addressing ways to improve the quality and provision of HIV CTR.