Assessment of adherence within AIDS clinical trials is a critical component of the successful evaluation of therapeutic outcomes. Poor medication adherence can result in the misinterpretation of clinical trial data. Research on factors affecting adherence in AIDS clinical trials has been scarce, and few investigations have evaluated strategies for enhancing patient participation. One reason may be the absence of a conceptual framework to guide research. Consistent with previous research on medical adherence, we propose a framework whereby factors affecting adherence in AIDS clinical trials can be categorized as characteristics of the: (a) individual, (b) treatment regimen, (c) patient-provider relationship, (d) clinical setting, and (e) disease. This framework is used as a heuristic for reviewing studies that examine factors affecting adherence in AIDS clinical trials. Suggestions for future research and clinical intervention are provided. These efforts are timely because adherence is now the center of attention in discourse about the efficacy of the new class of protease inhibitor drugs; non-adherence has been linked to viral resistance and drug failure. Efforts to identify factors that influence adherence to AIDS clinical trials can inform future attempts to improve adherence and retention. Better adherence protects the scientific integrity of AIDS clinical trials, promoting more efficient and accurate evaluations of therapeutic value. Accelerated access to new treatments may follow, ultimately enhancing patient care.