Background: Maintenance doses for AIT have been recommended for at least 3 years, little data on long-term efficacy is available depending on AIT duration. To show sustained efficacy 10 years after completion of treatment with depigmented-polymerized house dust mite (dpg-pol HDM) allergen extract in adults with asthma and/or rhinoconjunctivitis. Methods: Patients included in a double-blind placebo-controlled AIT study with dpg-pol HDM allergen extract were reviewed at completion of the perennial treatment and 10 years later (10y-FU). Change in symptom and rescue medication score was the primary objective. Visual analogue scale, asthma control test (ACT) and degree of disease control were secondary objectives. A comparative analysis between patients who underwent treatment for < 3 years and ≥ 3 years was performed. Results: Data from 31 patients (mean age 38 years) were available at 10y-FU. All had asthma and 29 had rhinoconjunctivitis at baseline. Twenty-three patients were treated ≥ 3y and 8 for < 3y. Seventeen (55%) patients were asymptomatic at completion AIT completion, with significant differences for nasal, conjunctival and bronchial symptoms (p<0.0001) compared to baseline only in patients treated ≥3y. Nine (52.9%) patients remained completely asymptomatic at 10yFU , all were treated for ≥ 3 years. Moreover, significant reduction in the number of patients with rhinitis (p=0.0117), conjunctivitis (p<0.0001) and bronchial (p=0.0005) symptoms was observed at 10y-FU compared to baseline only in the ≥3y treated. Ten (32.3%) patients didn´t require any rescue medication at 10y-FU, all had been treated for ≥ 3y. ACT at 10y-FU showed a good control of asthma (median 23.5; 95% IC[22.0, 25.0]). No significant differences were observed between VAS at end of treatment compared to VAS at 10y-FU. Conclusions: Sustained clinical efficacy is achieved 10 years after completion of depigmented-polymerized HDM, however these findings were observed only if patients are treated for at least 3 years.