Data support the link between adherence to HIV treatment and detectability of HIV RNA (a predictor of disease progression), making adherence a vital issue in HIV therapy. OBJECTIVE: To develop and assess a questionnaire to measure adherence to HIV treatment. METHODS: Items from two existing measures, the Patient Medication Adherence Questionnaire (PMAQ) and the Treatment Review and Satisfaction Questionnaire (TRaSQ), were tested and revised using feedback from focus groups and in-depth interviews with 28 US and 29 Italian HIV-infected patients. This assessment highlighted issues surrounding adherence, including patient beliefs, knowledge and attitudes, lifestyle changes, medication characteristics, regimen complexity, side effects, patient-provider relationships, and patient recall. The subsequent instrument, the PMAQ7, contains Likert-type items addressing these issues, and a behavioral assessment of adherence over the past 7 days. RESULTS: Patients indicated that the PMAQ7 addressed issues that were important to HIV patients, including side effects and convenience of regimens. They added that an issue’s importance could vary with the length of time that a patient has been on HIV treatment. In addition, cultural differences became apparent regarding issues such as privacy, which was of greater concern to Italian patients than US patients, and bureaucratic issues surrounding drug availability, which were difficult for some US patients but not for Italian patients. Finally, in response to patient suggestions, the questionnaire includes positive wording about “taking” rather than “missing” medication. CONCLUSION: In this small group of patients, the PMAQ7 was judged to be relevant for patients, offering a promising initial indication of the validity of the instrument to monitor and manage adherence to antiretroviral therapy.