Background: The knowledge of the natural history of asthma from birth to adulthood could provide important clues for its cause and for the understanding of epidemiologic findings. Objective: This study is aimed at assessing the incidence and remission of asthma from birth to the age of 44 years by using data from 18,873 subjects involved in a large, nationally representative, cross-sectional study carried out in Italy from 1998 through 2000. Methods: The onset of asthma was defined as the age at the first attack, and remission was considered present when a subject was neither under treatment nor had experienced an asthma attack in the last 24 months. Person-years and survival techniques were used for the analysis. Results: The average annual incidence rate for the 1953 to 2000 period was 2.56/1000 persons per year. Incidence peaked in boys less than 10 years of age (4.38/1000 persons per year) and in women 30 years of age or older (3.1/1000 persons per year) and showed a generational increase (incident rate ratio = 2.63 and 95% CI = 2.20-3.12 for 1974-1979 vs 1953-1958 birth cohort). The overall remission rate was 45.8% (41.6% in women and 49.5% in men, P < .001). Asthmatic patients in remission had an earlier age at onset (7.8 vs 15.9 years, P < .001) and a shorter duration of the disease (5.6 vs 16.1 years, P < .001) than patients with current asthma. The probability of remission was strongly ( P < .001) and inversely related to the age at onset (62.8% and 15.0% in the <10- and ≥20-years age-at-onset groups, respectively). Conclusion: With respect to its natural history, asthma presents 2 different forms: early-onset asthma, which occurs early in childhood, affects mainly boys, and has a good prognosis, and late-onset asthma, which generally occurs during or after puberty, mainly affects women, and has a poor prognosis. The minority of patients with early-onset asthma who do not remit represents more than 35% of patients with current asthma in the general young adult population. (J Allergy Clin Immunol 2002;110:228-35.)