OBJECTIVES:  We conducted a health economic evaluation of allergen immunotherapy with HDM SLIT-tablet for patients with house dust mite induced allergic rhinitis (AR) and for patients with allergic rhinitis plus allergic asthma (RA+AA) in an Italian setting. METHODS:  Analysis included patients and data taken from Regional Allergy Network of the Piedmont Region (RRA). We built a cost utility model with the aim to capture the costs and health consequences of treatment for HDM AR and AA plus AR patients. The following parameters were included: effectiveness of available treatment options; acquisition costs of treatment; symptomatic pharmacotherapy use and other healthcare resource use associated with the considered conditions; quality of life experienced by patientsA budget impact analysis was carried out to assess the annual cost of treatment per patient with HDM SLIT-TABLET as compared to patients receiving symptomatic pharmacotherapy only. The analysis estimated the total costs and QALYs for one hypothetical adult patient receiving HDM SLIT-TABLET in addition to symptomatic pharmacotherapy and one hypothetical adult patient receiving symptomatic pharmacotherapy only, over a ten-year period. RESULTS:  Regarding the cost-utility analysis, ICER values were found to be equal to € 73,254 for the first year, € 7,797 for the fifth year and € 3,456 for the tenth year for AR patients. The ICER values for AR plus AA were € 31,095 for the first year, € 6,254 for the fifth year and € 3,153 for the tenth year. The first year was the most critical one, due to the drug cost; starting from the first year for AR patient and from the second year for AA plus AR patients an acceptable ICER value was achieved, due to the improved quality of life. CONCLUSIONS:  Patients receiving HDM SLIT-TABLET in addition to symptomatic pharmacotherapy were cost effective as compared to patient receiving symptomatic pharmacotherapy only.