Meta-analysis is a powerful tool for evaluating the efficacy of a therapeutic intervention, and has clearly demonstrated that specific allergen immunotherapy (SIT) is effective for treating allergic rhinitis and asthma. Future research needs to focus on specifying the most effective forms of SIT for specific populations and allergens, using validated clinical outcomes, studying long-term outcomes (particularly the potential disease-modifying effect of immunotherapy), and assessing outcomes regarding health economics. The safety profile of SIT should be evaluated using international guidelines and terminology, and needs to include high-quality surveillance data.