Efficacy of allergen immunotherapy is evaluated by means of clinical symptoms score, medication score, their combination and results of functional tests of respiratory tract. Value of immunological markers is not established and still remains useful for the research purposes. Evaluation of clinical outcomes of allergen immunotherapy focuses on target organ of allergic inflammation, allergy profile, patient’s age, composition of allergen extract and its route of administration. Results of systematic reviews addressed to assessment of therapy outcomes of allergen immunotherapy confirm efficacy of allergen immunotherapy given both subcutaneously and sublingually in children and adults with atopic asthma, allergic rhinitis and allergic conjunctivitis sensitized to house dust mites, grass pollen or tree pollen.