Background: Pollen exposure has acute adverse effects on sensitized individuals. Information on the prevalence of respiratory diseases in areas with different pollen concentrations is scanty. Aim: We performed an ecologic analysis to assess whether the prevalence of allergic rhinitis and asthma in young adults varied across areas with different pollen concentrations in Italy. Methods: A questionnaire on respiratory diseases was delivered to random samples of 20-44 year-old subjects from six centers in 2005-2010. Data on the daily air concentrations of 7 major allergologic pollens (Poaceae, Urticaceae, Oleaceae, Cupressaceae, Coryloideae, Betula and Ambrosia) were collected for 2007-2008. Center-specific pollen exposure indicators were calculated, including the average number of days per year with pollens above the low or high concentration thresholds defined by the Italian Association of Aerobiology. Associations between pollen exposure and disease prevalence, adjusted for potential confounders, were estimated using logistic regression models with center as a random-intercept. Results: Overall, 8834 subjects (56.8%) filled in the questionnaire. Allergic rhinitis was significantly less frequent in the centers with longer periods with high concentrations of at least one (OR per 10 days = 0.989, 95%CI: 0.979-0.999) or at least two pollens (OR = 0.974, 95%CI: 0.951-0.998); associations with the number of days with at least one (OR = 0.988, 95%Cl: 0.972-1.004) or at least two (OR = 0.985, 95%CI: 0.970-1.001) pollens above the low thresholds were borderline significant. Asthma prevalence was not associated with pollen concentrations. Conclusions: Our study does not support that the prevalence of allergic rhinitis and asthma is greater in centers with higher pollen concentrations. It is not clear whether the observed ecologic associations hold at the individual level. (C) 2017 Elsevier B.V. All rights reserved.