Participants in a longitudinal cohort study (the National Child Development Study) were asked, at the age of 23, about their smoking habits and asthmatic experiences since 16 years of age. Of the total sample (n = 8860) 10.8% reported smoking cigarettes, and the percentages were very similar in the two sexes although males tended to be heavier smokers. There was an association between asthma and smoking; more than expected of those reported as having asthma at any age had smoked, and of those with asthma since 16 years of age more reported smoking than expected by chance. In addition, all who report asthma at any time since the age of 16 are overrepresented among those who report current smoking (p < 0.001). Those reporting asthma since 16 are more likely to be living with others who smoke, and their spouses or partners were more likely to be heavy smokers (30+ cigarettes per day). In addition, in more than the expected number of homes where asthmatics live, there are others who smoke (p < 0.003).