A report, published in the October issue of Diabetes Care, is among the first large-scale population-based studies to link diabetes prevalence with air pollution. It is consistent with prior laboratory studies finding an increase in insulin resistance, a precursor to diabetes, in obese mice exposed to particulates, and an increase in markers of inflammation (which may contribute to insulin resistance) in both the mice and obese diabetic patients after particulate exposure. Like the laboratory studies, the current study focused on fine particulates of 0.1-2.5 nanometers in size (known as PM2.5), a main component of haze, smoke and motor vehicle exhaust. The investigators, led by John Pearson and John Brownstein, PhD, of the Children’s Hospital Informatics Program, obtained county-by-county data on PM2.5 pollution from the EPA, covering every county in the contiguous United States for 2004 and 2005. Comment: It is important that terms be used correctly. A link implies cause and effect. This crossectional study can only show an association; that two items are found at the same time. Correcting for obesity clarifies little. There can be many reasons for such a coincidence, including genetics, migration, types of work that may attract more obese people and many other confounders. This seems more like a political study than an epidemiologic one.