Introduction. The poor long-term adherence is known to affect the efficacy of allergen immunotherapy (AIT). In the case of injection AIT (SCIT), one of the main determinants is the inconvenience for patients to undergo prolonged build-up phases. Thus, simplifying the time schedule of the induction protocol could be effective in increasing the adherence to SCIT. Methods. We backtracked the SCIT renewal orders, thanks to the cooperation of the manufacturing company, and we compared the long-term adherence of 152 patients, who were prescribed with an abbreviated build-up schedule (4 injections, allergoid) with that of 302 patients treated with the same product, but with the traditional build-up protocol (7 injections). Results. According to the patient-named refills, those patients on the abbreviated build-up were significantly more compliant at the 2nd and 3rd year of treatment compared to the other group (p=0.0001). The drop-out rate after one year was also significantly lower between the two groups (p=0.0001). In the abbreviated group, as expected, reimbursed patients showed significantly better adherence compared with patients with no reimbursement at all (p<0.05). Conclusions. Abbreviating the build-up phase by reducing the number of injections significantly improves patients’ adherence to SCIT.