Asthma is a common chronic disorder which may be increasing in prevalence. However, little is known of its distribution and determinants. The European Community Respiratory Health Survey (ECRHS) is a multicentre survey of the prevalence, determinants and management of asthma. This paper presents a descriptive account of the variation in self-reported attacks of asthma and asthma symptoms across Europe, and in part fulfils the first aim of the study. A screening questionnaire, including seven questions relating to the 12 month prevalence of symptoms of asthma, was distributed to representative samples of 20-44 year old men and women in 48 centers, predominantly in Western Europe. The median response rate to the questionnaire was 75% but, after removing from the denominator those who were the wrong age, were known to have moved out of the area, or had died, it was 78% (range 54-100). The prevalence of all symptoms varied widely. Although these were generally lower in northern, central and southern Europe and higher in the British Isles, New Zealand, Australia and the United States, there were wide variations even within some countries. Centres with a high prevalence of self-reported attacks of asthma also reported high prevalences of nasal allergies and of waking at night with breathlessness. The use of asthma medication was more common where wheeze and asthma attacks were more frequent. In most centres in The Netherlands, Sweden, New Zealand and the United Kingdom over 80% of those with a diagnosis of asthma were currently using asthma medication. In Italy, France and Spain the rate was generally less than 70%. These data are the best evidence to date that geographical differences in asthma prevalence exist, are substantial and are not an artefact of the use of noncomparable methods.