Even though obesity is a well-established risk factor of type 2 diabetes, there is emerging evidence that persistent organic pollutants (POPs), a variety of lipophilic chemicals accumulated in adipose tissue, may be critically involved in the pathogenesis of type 2 diabetes. Among various POPs, serum concentrations of organochlorine pesticides and polychlorinated biphenyls (PCBs) were the most strongly and consistently linked to type 2 diabetes in both cross-sectional and prospective studies. In particular, obesity did not seem to be related to type 2 diabetes among persons with very low serum concentrations of POPs, suggesting a more fundamental role of chlorinated POPs in the pathogenesis of type 2 diabetes. These POPs were also associated with obesity, insulin resistance, and adverse lipid profiles like high triglyceride and low high-density lipoprotein (HDL) cholesterol among persons without diabetes, all metabolic dysfunctions commonly observed before developing type 2 diabetes. Recent animal studies supported the findings from epidemiological studies. If all these findings on POPs are true, it suggests that any effort to reduce the external and internal exposure to POPs would be necessary to decrease the social burden of type 2 diabetes.