BACKGROUND: Global climate change concerns are forcing local public health agencies to assess potential disease risk. OBJECTIVE: Determine if risk of an emergency department asthma diagnosis in Douglas County, NE, was higher during the 2012 heatwave compared to 2011. METHODS: Retrospective, observational, case-control design selecting subjects from 2011 and 2012 emergency department (ED) admissions. Risk was estimated by conditional logistic regression. RESULTS: The asthma ED risk estimate was 1.23 (95%CI = 0.96-1.57) times higher in 2012 than 2011, for the same calendar period. Asthma ED diagnosis risk was 3.37 (95%CI = 2.27-4.17) times higher among subjects <19years old compared to older subjects, and 3.25 (95%CI = 2.63-4.02) times higher among African-Americans than non-African-Americans, adjusted for heatwave exposure. Absolute humidity appears inversely related to asthma diagnosis risk ( chi2 = 16.6; p < 0.001). CONCLUSION: Asthma ED diagnosis risk was not significantly higher in 2012 compared to 2011. Risk was elevated among subjects less than 19years old, and among African Americans; adjusted for heatwave exposure.