In recent years, several new studies have estimated the incidence of adult asthma. These studies vary in design and quality. The current paper summarises the findings of major population studies in the adult incidence of asthma. The pooled estimate of the adult incidence of asthma was 4.6 per 1000 person-years in women and 3.6 per 1000 person-years in men. The estimate among only general population cohort studies was higher, respectively 5.9 and 4.4 per 1000 person-years in women and men. The adult incidence of asthma was slightly higher in women than men. In the few studies that allowed the incidence of asthma to be estimated among those aged >50 years, there was a trend towards a higher incidence with age. It is thought likely that this is at least partly explained by misclassification with COPD. However, the current findings from these studies may imply that the incidence of asthma in the elderly has previously been under-estimated. Finally, the review shows that estimates of adult asthma incidence have tended to be higher in later studies, implying a rise in asthma incidence in adults within the timeframe of observation.