In the 11 years since AIDS became a defined disease, programs for the development and evaluation of new drugs for this disease have grown rapidly. Although the fundamental principles that drive the design, conduct, and analysis of clinical trials are as applicable to AIDS as to other diseases, there is no question that we have been confronted with unusually difficult challenges in studying therapeutic approaches for this disease. These include the multiple treatment needs of individual patients, identification of appropriate endpoints, rapidly changing “natural history,” and the need for interaction with an informed and vocal patient community that continues to express dissatisfaction with the pace of research. In this context, statisticians have taken a leadership role in identifying and addressing important methodological issues in the evaluation of AIDS drugs.