Methadone maintenance patients infected with human immunodeficiency virus (HIV) currently receiving antiretroviral therapy had HIV RNA testing and were surveyed regarding their adherence to their treatment regimens. Adherence was measured using self-report on four questions relating to medication use in the last day and last month and whether the patient took "drug holidays." Of the patients (N = 42), 52% were receiving two-drug antiretroviral therapy and 48% were receiving triple therapy that included a protease inhibitor. Persons on triple therapy reported higher rates of adherence on all measures and were more likely to have undetectable HIV RNA levels than persons on dual therapy (60% vs. 50%). Ongoing illicit drug injection was the only factor significantly associated (p < .05) with multiple measure nonadherence; however, it was not associated with undetectable HIV RNA level. Levels of nonadherence were comparable to estimates from other chronic diseases, but this finding has important implications for patients receiving highly active antiretroviral therapy.