Adherence counseling can improve antiretroviral adherence and related health outcomes in HIV-infected individuals. However, little is known about how much counseling is necessary to achieve clinically significant effects. We investigated antiretroviral adherence and HIV viral load relative to the number of hours of adherence counseling received by 60 HIV-infected drug users participating in a trial of directly observed antiretroviral therapy delivered in methadone clinics. Our adherence counseling intervention combined motivational interviewing and cognitive-behavioral counseling, was designed to include six 30 minute individual counseling sessions with unlimited "booster" sessions, and was offered to all participants in the parent trial. We found that, among those who participated in adherence counseling, dose of counseling had a significant positive relationship with antiretroviral adherence measured after the conclusion of counseling. Specifically, a liner mixed-effects model revealed that each additional hour of counseling was significantly associated with a 20% increase in post-counseling adherence. However, the number of cumulative adherence counseling hours was not significantly associated with HIV viral load, also measured after the conclusion of counseling. Our findings suggest that more intensive adherence counseling interventions may have a greater impact on antiretroviral adherence than less intensive interventions; however, it remains unknown how much counseling is required to impact HIV viral load.