Asthma and rhinitis are often comorbid conditions, and the overall characteristics of the diseases and the treatment options for the disorders are similar. Several recent epidemiologic studies in the general population have provided evidence to strongly associate the development of asthma with a previous history of either allergic or perennial rhinitis. Additional links between asthma and rhinitis include a description of increased aspirin intolerance in both disorders and the observation that most subjects with occupational asthma experience rhinitis. Further, the likelihood of the development of asthma is much higher in individuals with both perennial and seasonal rhinitis than for individuals with either condition alone. Asthma and rhinitis were found to be comorbidities regardless of atopic state, and perennial rhinitis has been associated with an increase in nonspecific bronchial hyperresponsiveness. Several studies have identified rhinitis as a risk factor for asthma, with the prevalence of allergic rhinitis in asthmatic patients being 80% to 90%. These studies and others demonstrate that the coexistence of asthma and allergic rhinitis is frequent, that allergic rhinitis usually precedes asthma, and that allergic rhinitis is a risk factor for asthma. Finally, studies that have examined the age of onset of atopy as a confounding factor for the development of asthma and allergic rhinitis have suggested that early age atopy may be an important predictive factor for respiratory symptoms that continue into late childhood. In conclusion, rhinitis and asthma are strongly associated, and rhinitis has been identified as a risk factor for asthma. (J Allergy Clin Immunol 2000;106:S201-5.)