OBJECTIVE: To assess the effect of the new American Diabetes Association (ADA) diagnostic criteria for diabetes in the Mexico City survey. METHODS: The data available from the Mexico City study were included. This cross-sectional survey was conducted from January 1991 to March 1992 and involved 805 adults (20 years of age or older; mean age, 41 years). Survey procedures and results were previously published. Of the residents with diabetes, 74.2% had a previous diagnosis, and 25.8% were diagnosed on the basis of fasting plasma glucose (FPG) levels obtained during the survey. For the current report, these data were reanalyzed on the basis of the new ADA diagnostic criteria. RESULTS: The prevalence of newly diagnosed diabetes with use of the old and the new criteria was 23.1% versus 32.3% in men (P = 0.31) and 27.5% versus 36.3% in women (P = 0.32), respectively. The crude prevalence rate of diabetes increased from 8.7% to 9.3% (P = 0.42), and the age-adjusted rate increased from 10.6% to 11.2% for women (P = 0.64) and from 6.0% to 6.5% for men (P = 0.49). The prevalence of impaired FPG was 4.8%. Those patients with impaired FPG or newly diagnosed diabetes with FPG levels between 126 and 140 mg/dL had a more atherogenic risk profile than did those with normal carbohydrate metabolism. CONCLUSION: On the basis of the 1990 population census in Mexico City, the new ADA criteria will add 28,331 patients with diabetes (6.9%) to an already insufficient medical system. For those patients with impaired FPG or newly diagnosed diabetes on the basis of the new criteria, management should be focused on the control of the diverse and highly prevalent coronary risk factors.