BACKGROUND Hypertension has recently been identified as the leading risk factor for global mortality. This study aims to present the national prevalence of hypertension and prehypertension and, their determinants in Vietnamese adults. METHODS Nationally representative data were obtained from the National Adult Overweight Survey 2005. This one visit survey included 17,199 subjects aged 25–64 years, with a mean body mass index (BMI) of 20.7kg/m2. RESULTS The overall census-weighted JNC7 (the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure) defined prevalence of hypertension was 20.7% (95% confidence interval (CI) = 19.4–22.1); the prevalence of prehypertension was 41.8% (95% CI = 40.4–43.1). Hypertension and prehypertension were more prevalent in men. Higher age, overweight, alcohol use (among men), and living in rural areas (among women) were independently associated with a higher prevalence of hypertension, whereas higher physical activity and education level were inversely associated. Age, BMI, and living in rural areas were independently associated with an increased prevalence of prehypertension. Among the hypertensives, 25.9% were aware of their hypertension, 12.2% were being treated, and 2.8% had their blood pressure under control; among the treated hypertensives, 32.4% had their blood pressure controlled.