The role of allergen-specific immunotherapy in asthma (AIT) is still a matter of debate. Actually, many controlled clinical trials have proved efficacy and safety of AIT in asthma, and some published meta-analyses, despite some methodological weaknesses, have confirmed these findings, the most recent and convincing being a meta-analysis on injection AIT studies. For sublingual AIT evidences do exist, but SLIT meta-analyses are mostly questioned due to some biases and inconsistencies. Most of these arise from methodological problems in single studies, usually small, underpowered and carried out with mixed populations. The main need, therefore, is to perform AIT clinical studies only in patients with asthma and following standardized protocols, as recommended by international Guidelines. Studies of AIT in asthma should also focus more on the long term and preventive effects of the treatment, rather than considering only the immediate efficacy on allergic symptoms. Furthermore, specific asthma features, such as lung function, bronchial reactivity, asthma control and exacerbations, should be included among the study outcomes.