The aim of this analysis was to estimate the geographical variation in the prevalence of physician-diagnosed asthma and treatment practice for asthma in young adults. The results are based on an ecological analysis of 34 centres in 14 countries, in which a total of 17,029 randomly selected subjects (52% females, age 20-48 yrs) underwent a structured interview and spirometry as part of the European Community Respiratory Health Survey. The sample was enriched with 2,903 symptomatic subjects when investigating treatment in subjects with physician-diagnosed asthma. The prevalence of physician-diagnosed asthma was highest in New Zealand and Australia (11-13%) and lowest in Erfurt, Germany (1.2%) and Spain (1.5-3.0%). The reported use of antiasthma medication in the last 12 months was also highest in New Zealand and Australia (12-16%) and correlated closely with the prevalence of diagnosed asthma (r=0.89, p<0.001). Herbal remedies against breathing problems had been used by 13% of subjects in Hamburg but the reported use of alternative remedies for breathing problems was low in most other centres. The use of inhaled anti-inflammatory drugs in subjects with physician-diagnosed asthma ranged from 49% in the UK to 17% in Italy and correlated with the prevalence of doctors' consultations within the last 12 months (r=0.66, p<0.05). The prevalence of anti-inflammatory treatment was positively related to the prevalence of nocturnal asthma symptoms (p<0.05). We conclude that there is a wide geographical variation in the prevalence of physician-diagnosed asthma and use of antiasthma medication. The geographical variation in the use of anti-inflammatory drugs among individuals with diagnosed asthma may be related to variations in asthma severity, as well as differences in treatment practices between countries.