To determine whether fasting glucose/insulin (FG/I) ratio and insulin levels 2 h after 75-g oral load of glucose (IL-2 h PG) are predictors for type 2 diabetes mellitus, a comparative 2 year follow-up study was conducted. Ninety-six healthy subjects 30 years of age or older, randomly selected from the general population of Durango, Mexico were included in two groups: 1) risk group: members had both baseline FG/I ratio and IL 2-h PG within the lower and upper quartile, respectively, and 2) control group, whose members had baseline FG/I ratio and IL 2-h PG within the second and third quartiles, respectively. Multivariate logistic regression was used to compute the relative risk for the development of type 2 diabetes. The family history of diabetes (RR 10.1; IC95% 2.7-15.8, p < 0.01), glucose intolerance (RR 9.8; IC95% 1.7-13.4, p < 0.01), abdominal obesity (RR 6.1; IC95% 1.5-10.1, p < 0.01), and the low FG/I ratio and high IL 2-h PG (RR 3.3; IC95% 1.4-8.2, p < 0.05) were strong predictors for type 2 diabetes. Critical values for predicting criteria of FG/I ratio and IL 2-h PG were of 4.0 y 180 microUI/ml, respectively. In conclusion, the measurement of FG/I ratio and IL 2-h PG is an accurate indicator for estimating the risk of developing type 2 diabetes.