Purpose: Allergen immunotherapy (AIT), when continued for 3 years, is the only diseasemodifying treatment for AR and asthma. Adherence is a key to ensure effectiveness, and poor adherence is a contraindication for AIT. The objective of this study was to evaluate realworld adherence to AIT with subcutaneous immunotherapy (SCIT) and sublingual immunotherapy (SLIT) preparations in patients allergic to grass or tree pollen. The impact of AIT on the consumption of asthma and rhinitis medication was also analyzed. Patients and Methods: In this retrospective cohort analysis of a German longitudinal prescription database, the adherence of a grass and tree pollen allergoid was examined and compared to two sublingual AIT tablets/drops. Patients receiving grass or tree allergen-specific immunotherapy prescriptions were compared with non-AIT patients receiving symptomatic allergic rhinitis (AR) and asthma prescriptions. The study endpoints included therapy adherence, AR progression, and asthma progression. Multivariate regression analyses were used to estimate the effects of SCIT or SLIT, adjusting for variables related to demographics and prescriptions. Results: SCIT adherence was 60.1-61.8% at 2 years and 35.0-37.5% at 3 years for the two allergens. SLIT adherence was distinctly lower (29.5-36.5% and 9.6-18.2%, respectively). Adherence in children was higher compared to adolescents or adults. All products were highly efficacious at reducing symptomatic AR medication consumption. SCIT also reduced asthma medication use for both allergens, whereas for SLIT these results were significant only for grasses but not trees. Conclusion: Subcutaneous AIT in a real-world setting achieved significantly higher adherence rates compared to sublingual administration. SCIT reduced the use of rhinitis and asthma medication significantly for both allergens, while SLIT reduced the use of rhinitis medication for both allergens and the use of asthma medication for grasses only.