Medication adherence among persons with HIV infection is important not only because of the effect of non-adherence on an individual's health but also because non-adherence can lead to medication-resistant viral strains. However, adherence to HIV medications is difficult due to complex dosing regimens and side effects. This paper is a qualitative analysis of HIV medication adherence among gay and bisexual methamphetamine-abusing men enrolled in an outpatient drug treatment research project. As part of an open-ended, semi-structured interview, 23 HIV-infected men discussed the effects of their methamphetamine use on their medication adherence. Substance-use barriers to adherence were coded into two main themes: (1) planned non-adherence and (2) unplanned non-adherence. Planned non-adherence was a strategy for coping with demanding HIV medication schedules, or was linked to sexual behaviours while using methamphetamine or to fears of interaction effects from mixing methamphetamine with HIV medications. Participants did not define their medication regimen adjustments as non-adherence but as a way to achieve a sense of control over their lives. Unplanned non-adherence was linked to methamphetamine-related disruptions in food and sleep schedules. Findings are helpful in designing culturally specific HIV medication adherence interventions for this population.