Several studies have shown the importance of adherence to highly active antiretroviral therapy (HAART) in achieving HIV-1 suppression. However, most have focused on naïve patients and do not assess the impact of HAART on viral load (VL). Our aim was to evaluate the effectiveness of an adherence program in a cohort of multitreated and poorly adherent patients. We performed a cohort study of all adult HIV-1 infected patients with detectable VL who were treatment experienced and poorly adherent to HAART, included in an adherence program since its introduction in 2009 (n=136). The adherence program consisted of a multidisciplinary team with a nurse who specialized in behavioral intervention, counselling on substance abuse, and motivational interviewing, as well as a social worker responsible for referring patients to local healthcare centers. Effectiveness was evaluated as percentage of patients with VL <50 copies/mL at week 48 by modified intent-to-treat (mITT) analysis. Initially, 76.6% of the patients had an adherence <30% according to the Simplified Medication Adherence Questionnaire (SMAQ). At 48 weeks, 48.1% of the patients had VL <50 copies/mL, and the adherence was >90% in 71% of the patients. In multivariate analysis, a ratio of bottle refill per month >0.9 during the study [odds ratio (OR) 14.3; 95% confidence interval (CI) 4.08-50.08, p<0.001] and being on a b.i.d. regimen (OR 12.5; 95% CI 1.81-86.4, p=0.010) were associated with an undetectable VL. In conclusion, the adherence program was successful in almost half of the patients, despite their long treatment experience and prior poor adherence. This strategy may help to prevent disease progression and the risk of HIV transmission in these patients.