The prevalence of allergic rhinitis (AR) is on the increase and this condition is frequently associated with asthma, thus leading to the concept that these two conditions are different aspects of the same disease. There is now accumulating evidence that AR often precedes the onset of asthmatic symptoms. This notion has important implications, not only for the diagnosis and management of these common allergic conditions but also for the potential progression of disease. Very little is known about the risk factors responsible for the progression of AR to asthma; current treatment options can control symptoms but do not prevent or cure the disease. However, there are recent data supporting the notion that it is possible to prevent new asthma cases by modifying the immune response and clinical outcome with allergen immunotherapy. This review article evaluates the impact of AR on the development of asthma, examines putative predictors for the progression of AR to asthma, and reviews recent, promising literature suggesting that early treatment of allergic individuals with immunotherapy may aid in asthma prevention.