Atopic dermatitis (AD, also known as atopic eczema) is driven by a complex relationship between genetic predisposition and environmental exposures. We sought to determine the impact of specific climatic factors on the prevalence of AD in the United states. We used a merged analysis of the 2007 National Survey of Children's Health (NSCH) from a representative sample of 91,642 children aged 0-17 years and the 2006-2007 National Climate Data Center and Weather Service measurements of relative humidity (%), indoor heating degree days (HDD), clear-sky UV indices, ozone levels, and outdoor air temperature. As a proxy for AD, we used an affirmative response to the NSCH survey question asking whether the participant's child has been given a doctor diagnosis of "eczema or any other kind of skin allergy" in the previous 12 months. In multivariate models controlling for sex, race/ethnicity, age, and household income, eczema prevalence was significantly lower with the highest-quartile mean annual relative humidity (logistic regression, adjusted odds ratio (95% confidence interval)=0.82 (0.71-0.96), P=0.01) and issued UV index (0.73 (0.64-0.84), P<0.0001), and with two other factors associated with increased UV exposure. Eczema prevalence was decreased with the highest-quartile air temperature (0.80 (0.70-0.92), P=0.002) but increased with third-quartile mean annual HDD (1.26 (1.11-1.43), P=0.0003). This study provides evidence of climate influences on the US prevalence of childhood eczema.