Objective To determine whether Mexican Americans have an increased incidence of non-insulin-dependent (type II) diabetes mellitus relative to non-Hispanic whites. Currently, no study has reported on the incidence of this disorder in Mexican Americans. Research Design and Methods We determined the 8-yr incidence of type II diabetes in 617 Mexican Americans and 306 non-Hispanic whites who participated in the San Antonio Heart Study, a population-based study of diabetes and cardiovascular disease. Forty Mexican Americans (6.5%) and 6 non-Hispanic whites (2%) developed type II diabetes, as defined by World Health Organization criteria. The age-adjusted ethnic odds ratio (OR; Mexican Americans/non-Hispanic whites) for diabetes incidence was 8.13 (95% confidence interval [C1] 1.10–59.9) in men and 3.62 (95% CI 1.37–9.55) in women. We adjusted for age, sex, ethnicity, body mass index, and level of educational attainment with multiple logistic regression analyses. Results Mexican Americans continued to show a statistically significant increase in diabetes incidence (OR 2.72, 95% CI 1.02–7.28). Obesity and age were also positively related to diabetes incidence in this analysis (P < 0.001). In addition, subjects with at least some college education had a lower incidence of diabetes than those with less than a high school education (OR 0.51, 95% CI 0.26–0.99). Conclusions The incidence of type II diabetes in Mexican Americans is greater than in non-Hispanic whites, a difference that is not explained by ethnic differences in obesity, age, or level of educational attainment.