Background: The association between smoking habits and asthma is complex because subjects with asthma could avoid smoking, whereas smoking could increase asthma severity or incidence. Purpose: The relation between asthma in childhood (0-10 years) and smoking initiation in the second decade (11-20 years) was investigated using the database of the Italian Study on Asthma in Young Adults, performed in 1998-2000 on people aged 20-45 years. Methods: The cumulative incidence of smoking initiation was compared among (1) subjects not reporting asthma attacks in the first 20 years of life (n = 17,384), (2) subjects reporting asthma onset in the first decade and no disease remission by the age of 20 years (n = 305), (3) subjects reporting asthma onset in the first decade and remission in the first and second decades (n = 573). Results: Among men, the cumulative incidence of smoking onset was higher among nonasthmatics (49%) than among asthmatics (35.6%), and intermediate among asthmatics with disease remission (44.2%) (p = .001). These differences were larger in males born between 1953 and 1965, and tended to decrease in males born between 1966 and 1979: cumulative incidence of smoking onset decreased from 54.3% to 43.8% in nonasthmatics, whereas it remained stable in asthmatics (from 36.8% to 35%). Women, instead, had similar cumulative incidence of smoking initiation, irrespective of asthma onset or remission (p = .849). Conclusion: Asthma in childhood reduces smoking initiation during the subsequent teenage in men, but not in women. This protective effect tends to fade when asthma remission occurs. In the last decades, smoking initiation has decreased among nonasthmatic males, but not among asthmatic males. © 2010 Society for Adolescent Health and Medicine.