Data from two companion surveys of Europeans, South Asians, and Afro-Caribbeans in west London were used. A total of 4,367 men and women aged 40-64 years who were not known to have diabetes underwent an oral glucose tolerance test after an overnight fast. The prevalence of undiagnosed diabetes was estimated using the ADA (fasting plasma glucose>or = 7.0 mmol/l) and WHO (2-h postload glucose>or = 11.1 mmol/l) criteria for epidemiologic studies