The present work aims to assess the international variation in the prevalence of chronic bronchitis and its main risk factor, smoking habits, in young adults of 35 centres from 16 countries. Respiratory symptoms and pulmonary function were assessed in 17,966 subjects (20-44 yrs), randomly selected from the general population, in the frame of the European Community Respiratory Health Survey. The median prevalence of chronic bronchitis was 2.6%, with wide variations across countries (p<0.001; 0.7-9.7%). The prevalence of current smokers ranged 20.1-56.9%, (p<0.001) with a median value of 40%. Current smoking was the major risk factor for chronic bronchitis, especially in males. Its effect increased according to number of pack-yrs: in males, the odds ratio of chronic bronchitis was 3.51 (95% confidence interval (CI) 2.31-5.32) in 1-14 pack-yrs smokers and increased to 17.32 (9.97-30.11) in > or = 45 pack-yrs smokers with respect to nonsmokers. Only 30% of the geographical variability in prevalence could be explained by differences in smoking habits, suggesting that other environmental and/or genetic factors may play an important role. In conclusion, chronic bronchitis is a substantial health problem even in young adults. The impressive prevalence in current smokers in most countries highlights the need to improve the quality of prevention.