The prevalence of atopy and related diseases is lower among children in Eastern European countries than in countries with a market economy. Such comparisons have not been made in adults. The European Community Respiratory Health Survey (ECRHS) postal questionnaire was mailed to random samples of 3000 inhabitants in Tartu, Estonia, and 3600 in Uppsala, Sweden, between the ages of 20 and 44 years. Asthmatic symptoms (wheeze with breathlessness occurring in the absence of colds) were less prevalent in Tartu (4.6% vs 6.8%, P < 0.001), as were attacks of asthma (1.9% vs 3.3%, P < 0.01), current asthma medication (0.7% vs 4.9%), and allergic rhinitis (17.8% vs 22.2%, P < 0.001). Age was inversely related to allergic rhinitis in Uppsala (P < 0.05), but not in Tartu. Nocturnal respiratory symptoms (wakening with chest tightness or being woken by an attack of breathlessness or an attack of cough) were more prevalent in Tartu (P < 0.001), and their prevalence increased with age (P < 0.05) in Tartu, but not in Uppsala. Symptoms of asthma and hay fever were less common but other respiratory problems more common in Tartu than in Uppsala. The difference in the prevalence of hay fever diminished with age, supporting the notion that the increasing prevalence of allergy among children and young adults in Western Europe is caused by a cohort effect.