Background: Ozone is a ubiquitous air pollutant with increasing concentrations in many populous regions. Toxicological studies show that ozone can cause oxidative stress and increase insulin resistance. These pathways may contribute to metabolic changes and diabetes formation. In this paper, we investigate the association between ozone and incident type 2 diabetes in a large cohort of African American women. Methods: We used Cox proportional hazards models to calculate hazard ratios (HRs) for incident type 2 diabetes associated with exposure to ozone in a cohort of 45,231 African American women living in 56 metropolitan areas across the United States. Ozone levels were estimated using the U.S. EPA Models-3/Community Multiscale Air Quality (CMAQ) predictions fused with ground measurements at a resolution of 12 km for the years 2007-2008. Results: The HR per interquartile range increment of 6.7 ppb of ozone was 1.18 (95% CI 1.04-134) for incident diabetes in adjusted models. This association was unaltered in models that controlled for fine particulate matter with diameter <2.5 pm (PM2.5). Associations were modified by nitrogen dioxide (NO2) levels, such that HRs for ozone levels were larger in areas of lower NO2. Conclusions: Our results provide initial evidence of a positive association between 03 and incident diabetes in African American women. Given the ubiquity of ozone exposure and the importance of diabetes on quality of life and survival, these results may have important implications for the protection of public health. (C) 2016 Elsevier Ltd. All rights reserved.