The purpose of this study was to compare and contrast three different methods for measuring self-reported antiretroviral medication adherence, correlate individual reports of adherence with measures of viral load, and identify the degree of concordance among self-reported medication adherence tools. Thirty-five adolescents between the ages of 11 and 21 years (mean age, 15.4) enrolled in National Cancer Institute (NCI) HIV primary treatment protocols participated in the study. Adherence approaches consisted of a clinical nurse rating (CNR), a Retrospective Self-Report Interview (RSI; using two different scoring criteria), and a 24-hour recall phone interview (Daily Phone Diary [DPD]). These were chosen because of their potential to be integrated within a clinical setting. Reported perfect adherence to protease inhibitors ranged from 31% to 54% depending on the measure used. There was little agreement between measures. Teenagers who reported perfect protease inhibitor adherence on both RSI-doses taken and DPD were approximately 5 times more likely to have a viral load less than 10,000 copies per milliliter. Advantages and disadvantages of each adherence method and clinical and research recommendations are discussed.