Physicians estimate their patients' adherence to medications, and base decisions about treatment on these estimates. In HIV, misjudgment of patient adherence can have adverse consequences, including withholding of therapy, unnecessary changes in therapy, or unnecessary laboratory testing. A review of the literature demonstrates that physicians are often inaccurate in estimating patient adherence with antiretroviral therapy. These findings have implications for practice. Standardized methods for adherence assessment are currently available that can be used to enhance physicians' ability to understand adherence behavior and barriers. The patient-physician relationship presents a unique setting for improving adherence. The authors propose interventions to improve adherence within the context of the patient-physician relationship at the physician level, interpersonal level, and organizational level. Improved communication, including discussion about patient lifestyle and preferences, can facilitate a frank exchange of information, negotiation, and a spirit of cooperation. Active patient participation in the decision-making process is crucial.