Introduction Allergen-specific immunotherapy (AIT) is a crucial therapy for allergic rhinitis. However, the long-term effectiveness of AIT remains to be explored. Aim To evaluate clinical and immunological long-term effects of sublingual allergen immunotherapy (SLIT) for common inhalant allergens in elderly patients with allergic rhinitis. Material and methods This trial was a prospective follow-up observation of patients with allergic rhinitis who completed SLIT for grass pollen or house dust mites (HDM). After 3 years of SLIT, 115 patients were compared to a placebo group during an additional 5 years of observation. The combined symptom medication score (SMS), quality of life and concentration of IgG 4 for Phleum pratense or Dermatophagoides pteronyssinus were monitored during the study. Results Five years after SLIT was discontinued, a significant clinical effect based on SMS was still observed compared with the baseline, just after SLIT and 5 years later as follows: 7.53 ±2.09 vs. 2.45 ±0.72 vs. 3.09 ±1.07 ( p < 0.05) for HDM and 8.19 ±2.41 vs. 3.05 ±1.62 vs. 4.47 ±2.31 ( p < 0.05) for grass pollen. Quality of life based on the Rhinoconjunctivitis Quality of Life Questionnaire was significantly improved in patients who received SLIT and remained at a good level after 5 years of observation. During the 5 years of observation after SLIT, there were no significant changes between specific IgG 4 levels and the analysed allergens compared to results just after SLIT. Conclusions The positive effect obtained after SLIT for grass pollen or house dust mites was sustained for a long period after AIT.