Allergic rhinitis (AR) is a common comorbidity of asthma that contributes to asthma severity. Although over 80 % of asthmatics have AR, the condition is frequently underdiagnosed in subjects with asthma. AR itself is also a highly prevalent condition, affecting 10-30 % of adults and up to 40 % of children. AR has been associated with both increased risk of asthma development and asthma severity. The exact mechanisms underlying these relationships have yet to be fully elucidated, but evidence supports a role for allergen sensitization. Compared to those with asthma alone, patients with comorbid AR and asthma have greater use of health care resources, including visits to the general practitioner, emergency department and hospitalizations. Pharmacological treatment of AR reduces this health care burden. Immunotherapy for AR improves both asthma and rhinitis symptoms in addition to preventing future allergen sensitizations and asthma development. Appropriate recognition, diagnosis and treatment of AR can significantly reduce asthma morbidity and improve quality of life.