<i>Background:</i> Subcutaneous immunotherapy for respiratory allergy has shown a long lasting efficacy after its discontinuation, whereas evidence in the case of sublingual immunotherapy (SLIT) is weak. This retrospective study evaluates whether SLIT exerts a long-lasting effect and whether it relates to its duration. <i>Methods:</i> Sixty-five patients allergic to mite and positive to methacholine challenge 13 years ago were studied. Twelve (control group, SLIT 0) were treated for 4 years only with standard pharmacological therapy (SPT), while 53 received SLIT and SPT. Among these, four groups were identified according to SLIT duration. Fifteen patients were treated for 1 year (SLIT 1), 10 for 2 (SLIT 2), 14 for 3 (SLIT 3) and 14 for 4 years (SLIT 4). Clinical parameters (symptom monthly score, SMS), bronchial reactivity and FEV₁ were evaluated in 1992 (run-in), 1993 (baseline) and every 2 years from 1997 to 2005. <i>Results:</i> Two to 3 years after the treatment ended, a positive effect on SMS, but not methacholine challenge and FEV₁, was seen in the SLIT groups versus SLIT 0. At this time interval an effect on methacholine challenge was also seen in SLIT 3. After 7–8 years a significant difference was seen for SMS, i.e., it was significantly better in SLIT 4 than in the other groups, while bronchial reactivity was still improved in SLIT 1, 3 and 4 only after 5–6 years. <i>Conclusions:</i>The effects of a 4-year SLIT on clinical parameters but not bronchial reactivity and FEV₁ last 7–8 years after its discontinuation. SLIT shorter than 4 years yields proportionally less impressive results.