Aim: We assessed the safety of allergoid adjuvanted by monophosphoryl lipid A (uSCIT-MPL-4) in a real-life setting. Materials & methods: Patients treated with uSCIT-MPL-4 were followed-up for 1 year. Systemic reactions (SRs) were registered and the association with potential risk factors was evaluated. Results: 2929 patients were included. Grade 0, 1, 2, 3 and 4 SR reactions were observed respectively in 3.3, 1.5, 0.31, 0.07 and 0.07% of patients. A significant association was detected between Grade ≥1 SRs and: female gender, number of administrations, previous local reactions. Conclusion: uSCIT-MPL-4 is safe. Local reactions should be accurately assessed as they may represent a risk factor for Grade ≥1 SRs, together with gender and number of doses/year.