OBJECTIVE: The aim of this study was to determine in Thai adults aged >or=35 years the prevalence and management of diabetes and the associations of diabetes with cardiovascular risk factors. RESEARCH DESIGN AND METHODS: The International Collaborative Study of Cardiovascular Disease in Asia was a complex sample survey. Data from a structured questionnaire, brief physical examination, and blood sample were collected from 5,105 individuals aged >or=35 years (response rate 68%). Population estimates were calculated by applying sampling weights derived from the 2000 Thai census. RESULTS: The estimated national prevalence of diabetes in Thai adults was 9.6% (2.4 million people), which included 4.8% previously diagnosed and 4.8% newly diagnosed. The prevalence of impaired fasting glucose was 5.4% (1.4 million people). Diagnosed diabetes, undiagnosed diabetes, and impaired fasting glucose were associated with greater age, BMI, waist-to-hip ratio, systolic blood pressure, total cholesterol, and serum creatinine levels. The majority of individuals with diagnosed diabetes had received dietary or other behavioral advice, and 82% were taking oral hypoglycemic therapy. Blood pressure-lowering therapy was provided to 67% of diagnosed diabetic patients with concomitant hypertension. CONCLUSIONS: Diabetes is common in Thailand, but one-half of all cases are undiagnosed. Because diagnosed diabetes is likely to be treated with proven, low-cost, preventive therapies such as glucose lowering and blood pressure lowering, initiatives that increased diagnosis rates would be expected to produce substantial health benefits in Thailand.