Allergen immunotherapy is effective in patients with allergic rhinitis (AR) and, unlike antiallergic drugs, has been shown to modify the underlying cause of the disease, with proved long-term benefits. Subcutaneous immunotherapy (SCIT) has been the gold standard, whereas sublingual immunotherapy (SLIT) has emerged as an effective and safe alternative. Previous Cochrane systematic reviews and meta-analyses have confirmed that both SLIT and SCIT are effective in patients with seasonal AR, whereas evidence for their efficacy in patients with perennial disease has been less convincing.