There are several reports showing that obese adults report more respiratory symptoms suggestive of asthma than those who are not obese. To determine the association of body mass index with respiratory symptoms and atopy in young adults Information collected from 15,454 participants in the European Community Respiratory Health Survey, a multicentre cross-sectional survey of young adults, was analysed to determine the association of body mass index with respiratory symptoms and atopy. Men and women with a body mass index of greater than 30 were at an increased risk of wheeze with shortness of breath compared with those with a body mass of 20-24.99 (OR in men 1.85, 95% confidence interval 1.41-2.42; OR in women 2.03, 95% confidence interval 1.59-2.58). Similar associations were observed for other symptoms suggestive of asthma. Body mass index was not associated with 'hayfever or nasal allergies', specific IgE to house dust mite, grass or cat or with total IgE in men or women. Reported associations of body mass index with symptoms suggestive of asthma are unlikely to be explained by a higher risk of atopy in the obese. Alternative explanations must be sought.