Résumé : Methadone Maintenance Treatment (MMT) program has been considered a medium through which human immunodeficiency virus (HIV) risks assessment and prevention on drug use/HIV-infected population can be effectively conducted. Studies concerning the implementation of such idea on patients in remote, under-developed areas, however, have been limited. Having the clinics established in three mountainous provinces of Vietnam, this study aimed to evaluate the changes in knowledge of HIV, perceived risk, and HIV testing uptake of the patients. A longitudinal study was conducted at six MMT clinics in three provinces with a pre-and post-assessments among 300 patients. Outcomes of interest were compared between baseline and after 12 months. The magnitude of changes was extrapolated. The proportion of participants reporting that their HIV knowledge was not good fell by 4.4% (61.3% at the baseline vs. 56.8% at 12 months). The significant improvement seen was in the knowledge that needle sharing was a mode of transmission (82.7% vs. 89.6%). Nevertheless, the majority of participants reportedly considered mosquitoes/insect and eating with the HIV-infected patient were the route of transmission at both time points (84.7% vs. 89.1%, 92.2% vs. 93.3%, respectively). This study found a limited improvement in HIV knowledge and testing uptake among MMT patients following a 12-month period. It also highlighted some shortcomings in the knowledge, attitudes and practices (KAP) of these patients, in particular, incorrect identification of HIV transmission routes, among patients both at program initiation and follow-up. The findings lent support to the argument for enhancing education and counseling efforts at MMT clinics regarding HIV, as well as for improving access to preventive and health care services through the integration of MMT/HIV services.