The authors recently observed that frequent paracetamol use was positively associated with asthma and rhinitis in young adults. Therefore, an ecological analysis was performed to measure international associations between paracetamol sales and atopic disease prevalences in children and adults. Published data from the International Study of Asthma and Allergies in Childhood (ISAAC) on the prevalence of four atopic symptoms in 13-14-yr-olds (112 centres) and 67-yr-olds (66 centres) in 1994/1995, and European Community Respiratory Health Survey (ECRHS) data on the prevalence of asthma symptoms, diagnosed asthma and rhinitis (44 centres), prevalence of atopy, mean bronchial responsiveness and mean total immunoglobulin E levels (34 centres) in young adults in 1991/1992, were used. Their associations with national 1994/1995 per capita paracetamol sales were measured using linear regression. Paracetamol sales were high in English-speaking countries, and were positively associated with asthma symptoms, eczema and allergic rhinoconjunctivitis in 13-14-yr-olds, and with wheeze, diagnosed asthma, rhinitis and bronchial responsiveness in adults. The prevalence of wheeze increased by 0.52% in 13-14-yr-olds and by 0.26% in adults (p<0.0005) for each gram increase in per capita paracetamol sales. These ecological findings require cautious interpretation, but raise the possibility that variation in paracetamol usage may explain some of the variation in atopic disease prevalence between countries.