To determine the best cutoff value of fasting plasma glucose (FPG) for diagnosis of diabetes, using the 2-h postglucose load (2-h PG) as the gold standard, in Mexican population and compare it to the 7.0 mmol/l limit proposed by the American Diabetes Association (ADA). 712 apparently healthy Mexican individuals were included in a cross-sectional randomized population survey. Sensitivity of FPG criterion for diagnoses of type 2 diabetes was calculated from a fourfold table. Glycemia value 2-h PG of >or=11.1 mmol/l was the "gold standard" diagnostic test. The optimal FPG value for diagnoses of diabetes was established on a receiver operating characteristic (ROC) scatter plot. On the basis of the "gold standard" diagnostic test, diagnosis of type 2 diabetes was established in 65 (9.12%) subjects, whereas the ADA FPG diagnostic criterion only identified 39 (5.47%) subjects; that is a sensitivity of 60% (CI(95%) 47.1-72.0). The ROC scatter plot showed the best cutoff value of FPG for diagnoses of diabetes that corresponds to 6.1 mmol/l, which has the highest sensitivity (0.985). FPG diagnostic criterion proposed by the ADA Expert Committee for diagnosis of type 2 diabetes has low sensitivity in Mexican population. For epidemiological purposes, estimates of diabetes prevalence in Mexico based on a FPG value of >or=6.1 mmol/l will improve the success of the screening.