Background: The success of subcutaneous immunotherapy (SCIT) mostly depends on regular injections. Our aim was to investigate adherence to SCIT with aeroallergens during the COVID-19 pandemic and demonstrate clinical consequences of treatment disruptions in real-life. Methods: Visual analogue scale for quality of life (VAS-QoL), VAS for symptom scores (VAS-symptom), medication scores (MSs) and total symptom scores (TSS-6) were recorded during the pandemic in 327 adult allergic rhinitis and/or asthmatic patients receiving maintenance SCIT and these scores were compared with the pre-pandemic data. Patients were grouped according to SCIT administration intervals; no delay (Group 1), <2 months (Group 2), and ≥2 month intervals (Group 3). Results: 104 (31.8%) patients (Group 3) were considered as non-adherent which was mostly related to receiving SCIT with HDMs and using public transportation for reaching the hospital. Median MS, VAS-symptom and TSS-6 scores of Group 3 patients during the pandemic were higher than the pre-pandemic scores (p=0.005, p<0.001, p<0.001, respectively) whereas median VAS-QoL scores of Group 3 during the pandemic were lower than the pre-pandemic scores (p<0.001). Median TSS-6 and VAS-symptom scores were the highest in Group 3 compared to other groups (p<0.001 for each comparison). Median VAS-QoL scores were the lowest in Group 3 compared to Group 1 and Group 2 (p<0.001, p=0.043, respectively). Conclusion: When precautions in allergy clinics are carefully applied, adherence to SCIT can be high during a pandemic. Patients must be warned about adhering to SCIT injections since delays in SCIT administration can deteriorate clinical symptoms.