BACKGROUND—The aim of the present study was to compare the prevalence of asthma among schoolchildren in 1978, 1991, and 1998 in Patras, Greece. METHODS—The study populations of the three comparable cross sectional surveys comprised third and fourth grade public school children in Patras, Greece. Sample sizes in 1978, 1991, and 1998 were 3735,2952 and 3397 children and response rates were 80.4%, 81.9%, and 90.6%, respectively. Prevalence of current, non-current, and lifetime asthma or recurrent wheezing was determined by parental questionnaire. Personal communication with the parents of asthmatic children in 1991 and 1998 provided data on lost schooldays. RESULTS—Prevalence rates of current asthma or wheezing in 1978, 1991, and 1998 were 1.5%, 4.6%, and 6.0%, respectively (1978-91: p=0.01, 1991-98: p=0.02, 1978-98: p=0.03). Lifetime prevalences of asthma or wheezing in 1991 and 1998 were 8.0% and 9.6%, respectively (p=0.03). Current diagnosed asthma increased proportionally to diagnosed wheezing during 1991-98. The number of schooldays lost in the previous 2 years because of asthma did not change (p>0.1) between 1991 (0.31 per child) and 1998 (0.34 per child). CONCLUSIONS—Our results support a true increase in the prevalence of current and lifetime asthma in the last 20 years among pre-adolescent children in Patras, Greece.