The Vietnamese South East Asian Nutrition Survey (SEANUTS), a cross-sectional study, was undertaken to assess the nutritional status in a nationally representative sample of children aged 0·5-11·9 years. A multi-stage cluster-randomised sampling method was used to recruit 2872 children. Anthropometric measurements included weight, height, mid-upper arm circumference, and waist and hip circumferences. Blood biochemistry involved analyses of Hb, serum ferritin, and vitamins A and D. Dietary intake was assessed using a 24 h recall questionnaire, and nutrient intakes were compared with the Vietnamese RDA. In children aged < 5 years, approximately 14% were stunted, 8·6% underweight and 4·4% thin. A higher prevalence of stunting (15·6%) and underweight (22·2%) was observed in school-aged children. Undernutrition was more prevalent in rural areas than in urban areas. In contrast, almost 29% of the urban children were either overweight or obese when compared with 4% of the overweight children and 1·6% of the obese children in rural areas. A higher percentage of children in the age group 0·5-1·9 years and residing in rural areas had low Hb levels than those in the age group 2·0-5·9 years and residing in urban areas. In children aged 6-11 years, a small percentage had low Hb (11-14%) and vitamin A (5-10%) levels, but almost half the children (48-53%) had vitamin D insufficiency. Food consumption data indicated that the children did not meet the RDA for energy, protein, Fe, vitamin A, vitamin B1 and vitamin C. Results from the SEANUTS highlight the double burden of malnutrition in Vietnam. Information from the SEANUTS can serve as an input for targeted policy development, planning and development of nutrition programmes.