Background: To sustain the long-lasting beneficial effects of allergen-specific sublingual immunotherapy (SLIT), an adequate duration of treatment is required. Nevertheless, many patients discontinue prematurely and therefore fail to obtain satisfactory therapeutic effect in clinical practice. The aim of this study was to analyze the causes leading to premature discontinuation of SLIT in allergic rhinitis (AR), and to provide the corresponding countermeasures for the following SLIT course. Methods: We performed a retrospective analysis of data from 142 patients with AR who started SLIT during the period from December 2009 to February 2015. Patients were contacted at 1, 3, 6, and 12 months into SLIT as part of our standard of care. The patients who claimed to have stopped treatment were asked to provide a reason during one of the phone calls. Results: Overall, 76 (54%) patients with AR terminated immunotherapy during the first year of treatment. Among the 76 patients, the following reasons were cited for nonadherence to immunotherapy: patients could not be reached (25%); ineffectiveness (24%); the long course (18%); improvement of symptoms (13%); side effects (4%); lack of confidence in the treatment (4%); or other reasons (12%). Conclusion: Fifty-four percent of AR patients terminated their treatment within the first year of SLIT. The top reasons for treatment discontinuation included patients not be reached, ineffectiveness, and length of course. (C) 2017 ARS-AAOA, LLC.