Through the efforts of thousands of individuals, the World Wide Web has become a gold mine of information about HIV. In this article, we describe approximately 90 Web sites that are among the most useful to clinicians and researchers with regard to HIV. Web sites were classified according to their content and target audience and were judged according to their adherence to accepted standards of medical Internet publishing. Selected Web sites were categorized into the following groups: (1) sites with comprehensive coverage of HIV treatment and its management, (2) on-line peer-reviewed journals, (3) proceedings of scientific meetings, (4) sites with HIV-related textbooks, manuals, and guidelines, (5) government publications, (6) research databases, (7) information on clinical trials, (8) sites with comprehensive information for laypersons, and (9) sites with information related to specific medical complications of HIV infection.