Plain language summary Hay fever has become more frequent over the years, and allergen immunotherapy (AIT) remains the only treatment able to reduce both symptoms and the root cause of this condition. However, it is not clear whether the benefits outweigh the price of the therapy. In this study, we observed patients in the common practice and described the effectiveness, safety and costs of injected AIT for pollen-induced hay fever. Of 471 new AIT users, 317 completed three courses of treatment in 3 consecutive years. Symptoms improved in 96% of them; no serious adverse reactions were reported. The cost of symptom-relieving medication decreased by 49% and the cost of unscheduled physician visits decreased by 73%. Except for costs related to AIT administration, total healthcare costs decreased by 54% compared with the years before AIT. In clinical practice, injected AIT is an effective treatment which generates savings on other medication and unscheduled physician consultations. Tweetable abstract In Czech clinical practice, subcutaneous allergen immunotherapy is an effective treatment for allergic rhinoconjunctivitis, generating savings on symptomatic medication and unscheduled physician consultations. Background: The prevalence of allergic rhinoconjunctivitis (AR) has been increasing over the years, and allergen immunotherapy (AIT) remains the only disease-modifying treatment. However, cost-effectiveness data remain scarce. Methods: In this single-arm, noninterventional, prospective, multicenter study, we describe the effectiveness, safety and costs of subcutaneous AIT for pollen-induced allergic rhinoconjunctivitis. Results: Of 471 new AIT users, 317 completed three courses of treatment, and symptoms improved in 96%; no serious adverse reactions were reported. The cost of symptomatic medication decreased by 49% and the cost of unscheduled specialist visits decreased by 73%. Except for AIT administration, total healthcare costs decreased by 54% compared with the baseline pollen season without AIT. Conclusion: In clinical practice, subcutaneous AIT is an effective treatment generating savings on symptomatic medication and unscheduled consultations.