BACKGROUND: Virological suppression is the main goal of antiretroviral therapy. To achieve this goal, efficient interventions that promote treatment adherence are needed. This study was aimed at exploring the impact of peer-education on virological outcomes in Northern Nigeria. METHODS: A randomized controlled trial (RCT) among patients receiving antiretroviral treatment was conducted in 2 phases between August 2006 and January 2008 in the "largely Muslim" Northern Nigeria. Participants were randomized into one of three intervention arms: standard of care arm, a second arm which included daily reminders via alarm and follow-up calls from peer-educators, and adherence support by a home-based treatment partner; and a third arm which included second arm activities, plus home visits by peer-educators. We evaluated sociodemographic factors and adherence levels, measured using self-report and pharmacy (Rx) refill rates, as risk factors for viral load (VL) suppression. RESULTS: Of the 600 participants (43% males), 276 were observed till the end of the study. There were no significant differences in mean log 10 VL between the intervention groups. At the end of entire follow-up period, 83% (229/276) who were not lost to follow-up achieved undetectable VL (< 400 copies/ml). In the multivariable analysis, age between 30-34 years (vs 18-24 years) and both baseline CD4 ranges between 100-199 cells/mm(3) or 200-349 cells/mm(3) (vs CD4 <100 cells/mm(3)) as positively associated with VL suppression while poor self-reported adherence and <95% Rx refill rates were negatively associated with VL suppression. CONCLUSION: High levels of viral suppression and low prevalence of drug resistance mutations (DRMs) were seen in this cohort participating in an ART adherence study in Northern Nigeria. Self-reported good adherence and optimal Rx refill rates were reported as significant predictors of VL suppression. Our findings indicate that ART adherence will improve significantly regardless of whether HIV-infected adults received peer-education-based medication adherence interventions or standard of care services.