Background The metabolic syndrome (MS) is characterized by a specific clustering of risk factors, including dyslipidemia, central adiposity, systemic hypertension, insulin resistance, and dysglycemia. It is associated with an increased risk of developing cardiovascular disease (CVD). Accurate data on prevalence and characteristics of MS will facilitate the development of preventive strategies for CVD. Objective To estimate accurately the prevalence of MS among Vietnamese adults with the usual criteria or with the criteria modified for Asian populations. Design and methods We studied a representative, cross-sectional, population-based sample of 856 subjects (mean age 52.82 ± 16.36) classified in three age groups from 15-34 years, 35-54 years and ＞ 54 years of age, living in Khanh Hoa Province, Viet Nam. MS was diagnosed according to the criteria defined by the Third Report of the National Cholesterol Education Program Expect Panel on Detection, Evaluation and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel Ⅲ) (NCEP-ATP Ⅲ) and by the modified criteria for some Asian populations in which the waist circumference (WC) is considered abnormal if it is ＞ 90 cm for males and ＞ 80 cm for females.Results Using the NCEP-ATP Ⅲ criteria, the prevalence of MS in the studied population was 10.0％ (CI 95 ％:8.1-12.3). It was 2.4 ％ in the 15-34 age group (men 4.5％ and women 1.2％),5.2％ (men 6.3％,women 4.5％ ) in 35-54 age group and 15.8％ (men 9.7％, women 21.7％) in over 54 age group, respectively. And it was more common in women than in men (11.7％ vs 8.0％, P ＜0.001). Using 2001 population census data of the whole province over 15 years (695 218 habitants) we estimated that about 35 193 people suffered from the MS.The WC was the least common feature of MS (2.1％ for men and in 6.1％ for women).Overall,45.2 ％ of the studied population had one feature of MS, 23.1％ had two features, 8.2％ had three features, 1.6％ had four features, and 0.2％ had all five features. No feature of MS was identified in 21.7％.Using the modified criteria,the prevalence of MS in the studied population was 15.7％. It was 4.0％ in the 15-34 age group, 12.5％ in the 35-54 age group and 21.5％ in the＞54 age group. Prevalence of modified WC feature was 10.9％ for men and 23.6％ for women.Conclusions MS is more accurately identified among Vietnamese adults using the modified criterion of the WC for some Asian populations. Its prevalence is similar to that in the developed countries. ( J Geriatr Cardiol 2004;1(2) :95-100.)