The objective of our study was to investigate factors associated with virological failure in 100 consecutive HIV-1 infected Vietnamese adults who initiated antiretroviral therapy (ART) from June 2007 to June 2008. Data were collected from medical records, and a structured questionnaire was used in individual interviews to investigate factors associated with adherence to ART. Plasma HIV viral load was measured at the time of the interview. The median age was 35 years, 35% were women and heterosexual intercourse was the most common mode of HIV transmission (61%). After a median of 14 months since starting ART, 23% had detectable HIV-1 viral load (≥ 400 copies/mL). Patients who had developed a World Health Organization (WHO) clinical stage 4 condition at the time of initiation of ART were more likely to experience virological failure than those in stages 1-3, odds ratio (OR): 5.20 (95% confidence interval [CI] 1.34-20.11), P = 0.017. Patients who reported that their health status was evaluated by a physician at each visit were less likely to experience virological failure, OR: 0.02 (95% CI 0.00-0.24), P = 0.002.