The incidence and prevalence of allergic diseases are constantly increasing in our times. The only etiologic treatments currently available are allergen avoidance and immunotherapy. Many scientific data demonstrate that immunotherapy with allergens is an effective and safe treatment for allergic rhinitis and asthma in adequately selected patients and that it reduces treatment costs for the patients in the long run. Other promising aspects of immunotherapy are its capacity to produce prolonged clinical remissions over time, that it is the only treatment capable of stopping the natural development of the respiratory allergic disease, and the possibility that immunotherapy could avoid evolution to asthma in a significant percent of patients with rhinitis.