The prevalence of asthma increased worldwide until the 1990s, but since then there has been no clear temporal pattern. The present study aimed to assess time trends in the prevalence of current asthma, asthma-like symptoms and allergic rhinitis in Italian adults from 1990 to 2010. The same screening questionnaire was administered by mail or phone to random samples of the general population (age 20-44 yrs) in Italy, in the frame of three multicentre studies: the European Community Respiratory Health Survey (ECRHS) (1991-1993; n = 6,031); the Italian Study on Asthma in Young Adults (ISAYA) (1998-2000; n = 18,873); and the Gene Environment Interactions in Respiratory Diseases (GEIRD) study (2007-2010; n = 10,494). Time trends in prevalence were estimated using Poisson regression models in the centres that repeated the survey at different points in time. From 1991 to 2010, the median prevalence of current asthma, wheezing and allergic rhinitis increased from 4.1% to 6.6%, from 10.1% to 13.9% and from 16.8% to 25.8%, respectively. The prevalence of current asthma was stable during the 1990s and increased (relative risk 1.38, 95% CI 1.19-1.59) from 1998-2000 to 2007-2010, mainly in subjects who did not report allergic rhinitis. The prevalence of allergic rhinitis has increased continuously since 1991. The asthma epidemic is not over in Italy. During the past 20 yrs, asthma prevalence has increased by 38%, in parallel with a similar increase in asthma-like symptoms and allergic rhinitis.