Previous observations have shown that the syndrome of thyroid autoimmunity and idiopathic urticaria and angioedema (ICUA) can be associated with a marked worsening of reactive airway disease. Possibly, mediators released in this syndrome may contribute to acute bronchospasm and associated respiratory symptoms in some patients. In this study, two patients presenting with overlapping clinical presentations of the syndrome of thyroid immunity and ICUA are described in whom a diagnosis of anaphylaxis to food and antibiotics, respectively, was initially suspected but ruled out by testing and challenges. These cases illustrate clinical overlap between presentations of ICUA and anaphylaxis. We suggest that patients with idiopathic anaphylaxis be evaluated for the presence of antithyroid microsomal (peroxidase) antibodies or antithyroglobulin antibodies, particularly because the diagnosis of thyroid antibody-positive ICUA may suggest additional therapeutic options.