Background: Allergen-specific immunotherapy (AIT) is safe and effective for the treatment of allergic rhinitis and allergic asthma. However, patient non-compliance is a major barrier to achieving optimal outcomes Objective: To determine the level of compliance among patients using AIT and to identify factors associated with non-compliance Methods: A retrospective analysis using questionnaires was conducted to study compliance among 236 patients with allergic rhinitis with or without asthma who began AIT in 2009 or 2010 Results: The compliance rates at 3 y were 58.7% among patients on subcutaneous immunotherapy (SCIT) and 11.6% among those on sublingual immunotherapy (SLIT). The mean durations of treatment with SCIT and SLIT were 31 (+/-18.3) and 15.9 (+/-14.7) months, respectively. The most common causes of non-compliance among patients on SCIT were the frequency of injections (82.2%), the duration of treatment (70.9%), and commuting to the Allergy Center (67.7%). Reasons for non-compliance among patients on SLIT were related to inconvenience (43.4%), improvement without treatment (30.2%) and perception of poor efficacy (25.0%) Conclusion: Compliance with AIT is low, but at 3years, it was higher among patients on SCIT than among patients on SLIT. Reasons for non-compliance include difficulty adjusting to treatment protocols and a perception that the efficacy is low. Patient education regarding the treatment course and the slow effect, as well as the need for close follow up to effectively prevent and treat adverse reactions, are important factors for improving compliance and treatment outcomes.