Serum concentrations of persistent organic pollutants (POPs) have been reported to be associated with the prevalence of type 2 diabetes in the U.S. general population, and this association appears to be higher among obese people than among the nonobese. However, because most previous studies were cross-sectional and because studies among subjects with high POPs exposure reported inconsistent associations, Lee et al. (p. 1235) investigated whether several POPs prospectively predict type 2 diabetes within the Coronary Artery Risk Development in Young Adults (CARDIA) cohort. The authors report that some POPs, such as trans-nonachlor and highly chlorinated polychlorinated biphenyls, were associated with incident type 2 diabetes over an 18-year period, especially in obsese people. However, POPs did not show a traditional dose–response relation with diabetes. Instead, POPs showed strong associations at relatively low exposures, resulting in inverted U-shaped dose– response curves. The authors conclude that exposure to relatively low concentrations of certain POPs may a play a role in the increased incidence of diabetes in the United States.