OBJECTIVES: The objectives of this study were to describe and compare adherence rates and to determine what factors are related to adherence to therapy among patients living with HIV/AIDS receiving Highly Active Antiretroviral Therapy (HAART) in a treatment center in Lagos, Nigeria. METHODS: Patients in the study were living with HIV/AIDS, 18 years or older, receiving HAART, and had visited the clinic between June and July 2012. Adherence was measured using two self-reported measures: number of doses taken over the past two weeks/number of doses provided over the past two weeks and the valid and reliable Morisky scale. Barriers, satisfaction with therapy, and sociodemographic and clinical variables served as independent variables. Data were collected via self-administered surveys. Descriptive statistics, Pearson’s correlation, McNemar’s test, Pearson’s chi-square test, analysis of variance, and logistic regression were used to address study objectives. RESULTS: The majority of the study sample (N=361) were between 18 and 40 (64.9%), female (58.3%), married (64.8%), working (83.8%), and on HAART for at least one year (82.0%) while a plurality of the sample had a college education (46.5%). Most of the patients (79.5%) reported 100% adherence using two-week self-recall and 49.6% using the Morisky scale. Both methods used to measure adherence were significantly correlated (rho=0.476; p<0.001). The significant (p<0.01) barriers to adherence between those 100% and <100% adherent were forgetfulness, running out of medication, alcohol use, and medication side effects. Multivariate logistic regression analysis showed that for every unit increase in the number of barriers, patients were 60.8% less likely to be 100% adherent (p<0.001, OR=0.392, 95% CI=). CONCLUSIONS: Interventions should target helping patients cope with forgetfulness, specifically employing strategies to overcome busyness in schedules, being away from home and tiredness.