Chronic idiopathic urticaria (CIU) is a common and frustrating disorder. A subset of patients with CIU has been classified as autoimmune on the basis of two main findings: association with thyroid autoimmunity and anti-IgE and/or anti-IgE receptor antibodies. There is growing evidence that some cases of CIU are associated with thyroid autoimmunity. Patients with CIU have an increased frequency of Hashimoto thyroiditis with the presence of antibodies to thyroglobulin or a microsomal-derived antigen (peroxidase), even in euthyroid patients. No broad non-specific autoimmunity is present. Antibodies reactive with Fc(epsilon)RI, the high-affinity IgE receptor are found in sera of 10-40% of patients with CIU. A smaller subset of patients with CIU lack anti-Fc(epsilon)RI antibodies and have anti-IgE antibodies that cross-link Fc(epsilon)RIs occupied by IgE. There are a minority of CIU patients that lack such antibodies, but can degranulate basophils by a serum factor that has not yet been determined. Most patients with anti-IgE antibodies have an IgG antibody directed against the 34 kd alpha subunit of the IgE receptor. There are no data to suggest that any of the anti thyroid antibodies is pathogenic in terms of CIU, and most likely these are associated, parallel, autoimmune events. Screening for thyroid autoimmunity and function is advisable in all patients with CIU for the early identification of patients requiring either treatment of underlying thyroid dysfunction or follow-up.