Aims/hypothesis. To estimate the prevalence of diagnosed and undiagnosed diabetes and impaired fasting glucose in the general adult population of China. Methods. The International Collaborative Study of Cardiovascular Disease in ASIA, conducted from 2000 to 2001, included a nationally representative sample of 15 540 adults, aged 35 to 74 years. An overnight fasting blood specimen was collected to measure serum glucose and information on history of diabetes and use of hypoglycaemic medications was obtained by a standard questionnaire. Undiagnosed diabetes (fasting glucose ≥7.0 mmol/l) and impaired fasting glucose (6.1-6.9 mmol/l) were defined using the American Diabetes Association criteria. Results. Prevalence of self-reported diagnosed diabetes, undiagnosed diabetes, and impaired fasting glucose in Chinese adults were 1.3%, 4.2%, and 7.3%, respectively. Overall, 5.2% or 12.7 million men and 5.8% or 13.3 million women in China aged 35 to 74 years had diabetes (self-reported diagnosis plus undiagnosed diabetes). The age-standardized prevalence of diabetes was higher in residents of northern compared to southern China (7.4% vs 5.4%, p<0.001) and in those living in urban compared to rural areas (7.8% vs 5.1%, p<0.001). Conclusions/interpretation. Our results show that the prevalence of diabetes in the adult population in China is much higher than previously reported. Three out of every four diabetes patients are undiagnosed, indicative of a lack of population-based screening programmmes and a relatively rapid and recent increase in incidence of diabetes. These results indicate that diabetes has become a major public health problem in China and underscore the need for national strategies aimed at prevention and treatment of diabetes. [Diabetologia (2003) Diabetes is a well-established modifiable risk factor for cardiovascular and renal diseases in Western countries [1,2]. The importance of diabetes is likely to increase because the prevalence of diabetes, particularly Type 2 diabetes, has risen steadily during recent decades and is projected to continue to increase. The prevalence of diabetes in a recent survey in the U.S. was 7.8% in adults aged 20 years and older, with a further 6.9% recording an impaired fasting glucose concentration [3]. The increasing prevalence of diabetes in the U.S. population contrasts with the observed decline in the prevalence of hypertension and hypercholesterolaemia in the same populations [4,5]. The rising prevalence of obesity, related to caloric intake in excess of energy expenditure, is a likely cause for