Exposure to fluoroquinolone antibiotics is postulated as a risk factor for subsequent development of type 2 diabetes. It is hypothesized that fluoroquinolones induce an intracellular magnesium deficit that can lead to insulin resistance. A temporal correlation is reported between the rate of outpatient prescription of quinolones and the incidence of diabetes during the period 1980-2011 with a lag of approximately two years (R(2)=0.86, P<10(-9)). The increase in incidence of diabetes after 1990 and the recent decrease in the number of new cases are both reflected in the fluoroquinolone prescription rates. A geographical correlation is reported (adj. R(2)=0.7, P<0.0001) between rates of increase in prevalence of diabetes in each U.S. state and a model using only local rates of outpatient fluoroquinolone prescription, local rates of increase in the prevalence of obesity, and local rates of population growth as predictor variables. Prescription rates of non-quinolone antibiotics correlated less well with the local rates of increase in prevalence of diabetes. The data are consistent with fluoroquinolone exposure predisposing an individual to develop diabetes with a probability that strongly depends upon factors that also lead to an increase in obesity. According to the hypothesis, much of the increase in the incidence of type 2 diabetes in the U.S. from 1990 to the present can be attributed to fluoroquinolone exposure.