The sublingual route has become an interesting and novel therapeutic option for the immunotherapeutic management of patients with allergies. Immunotherapy modifies the immune response by decreasing the specific IgE levels and Th2-type inflammation in the mucosa when allergen exposure occurs, shifting this toward a Th1-type response. Credible evidence exists of both effectiveness and safety of sublingual immunotherapy (SLIT) from several placebo-controlled double-blind studies. SLIT has been shown to be an effective treatment of allergic rhinitis and asthma in both children and adults. The therapy is well tolerated with mainly minor gastrointestinal side effects that subside in few weeks. The ideal treatment length and dosage still require further verification. Additional studies evaluating long-term efficacy and the immune response of SLIT still need to be performed, and additional standardized antigens still need to be developed.