In the last decade of the 20th century, cardiovascular disease was the leading cause of death in China, accounting for one-third of the total deaths. In comparison with western populations, the mean body weight or body mass index (BMI) of the Chinese population was lower, but showed an increasing trend. Whether the variation within lower levels of BMI or waist circumference was associated with other risk factors of cardiovascular disease, and whether they contribute independently to the risk of cardiovascular disease in the Chinese population, was investigated in this study. In keeping with a uniform study design, in each of 14 study populations at different geographical locations and with different characteristics, the incidence rates of stroke, coronary heart disease (CHD) and the causes of death were monitored in approximately/= 100000 residents from 1991 to 1995 using the MONICA procedure. Risk factors were surveyed in a random cluster sample of 1000 subjects (35-59 years of age) from each population under surveillance using internationally standardized methods and a centralized system to ensure quality control. Among the risk factors, body weight, height, and waist and hip circumferences were measured. Cross-sectional stratified analyses were used to analyse the relationship of BMI (kg m(-2)) or waist circumference to other metabolic risk factors. Ten cohorts among the 14 study populations with 24734 participants were surveyed from 1982 to 1985 as a baseline for further study and were followed-up for 9 years taking the events of stroke, CHD and different causes of death as end-points. Cox regression models were used to explore the association of BMI with the relative risks of stroke, CHD and total death. The survey in 14 random samples with a total number of 19 741 subjects showed that the mean BMI (20.8-25.1) and waist circumference (67.8-86.7 cm) were much lower than those of western populations. There was, however, variation in the anthropometric measurements among populations within China. Thus, rates of overweight varied from 2.7% to 48.1% and obesity from 0% to 9.5% on the basis of the World Health Organization (WHO) classification, but these values were lower than those found in western populations. Data from the 10 cohort samples compared with baseline data in the early 1980s showed that the mean BMIs increased significantly in eight populations during the early 1990s with the differences ranging from 0.5 to 2.5 kg m(-2). Despite the lower level of BMI and the lower rate of overweight, cross-sectional analyses showed that the prevalence of hypertension, high fasting serum glucose, high serum total cholesterol and low high-density lipoprotein cholesterol (HDL-C) and their clustering were all raised with increases in BMI or waist circumference. The prospective cohort study showed that the BMI was one of the independent risk factors for stroke and CHD in Chinese populations. Hence, in a Chinese population characterized by lower levels of BMI and great variability in rates of overweight, variation of BMI was significantly related to the prevalence of other metabolic risk factors and their clustering. Overweight was one of the independent risk factors for stroke and CHD, both at population and individual levels. Given the increasing trends of BMI in the last 10 years, during the period of economic transition there is a need to encourage the population to adopt healthy dietary habits and to increase their physical activity. Health education and health promotion are important for the prevention and non-pharmacological therapy of cardiovascular disease in China.