A large number of trials show that the anti-immunoglobulin (Ig) E antibody omalizumab is very effective in patients with severe allergic asthma. This is acknowledged in consensus documents. The drug also has a good safety profile and a pharmacoeconomic advantage due to a reduction in the number of hospitalizations for asthma attacks. In recent years, some studies have shown that omalizumab is effective also in nonallergic asthma. Effects on the complex signaling mechanisms leading to activation of effector cells and to mediator release may account for this outcome. Indeed, omalizumab has been reported to be effective in a number of IgE-mediated and non-IgE-mediated disorders. Concerning the former, clinical efficacy has been observed in rhinitis, allergic bronchopulmonary aspergillosis, latex allergy, atopic dermatitis, allergic urticaria, and anaphylaxis. In addition, omalizumab has been demonstrated to be able to prevent systemic reactions to allergen immunotherapy, thus enabling completion of treatment in patients who otherwise would have to stop it. Concerning non-IgE-mediated disorders, omalizumab has been reported to be effective in nasal polyposis, autoimmune urticaria, chronic idiopathic urticaria, physical urticaria, idiopathic angioedema, and mastocytosis. Current indications for treatment with omalizumab are confined to severe allergic asthma. Consequently, any other prescription can only be off-label. However, it is reasonable to expect that the use of omalizumab will be approved for particularly important indications, such as anaphylaxis, in the near future.