Chronic urticaria is a frequent pathology, characterized by the presence of hives and/or angioedema lasting longer than 6 weeks. In an important number of patients it behaves as an autoimmune illness, frequently associated with alterations in thyroid function and thyroid antibodies. We herein describe a consecutive series of 70 patients with a diagnosis of chronic urticaria. Seven (10%) had a diagnosis of thyroid illness previous to their first consultation. Thyroid function and thyroid antibodies were studied in the remaining 63 patients by measuring the level of serum thyrotropin and the titer of peroxidase antibodies. Abnormal thyrotropin levels were detected in 11 (17%) patients, who in conjunction with the 7 patients with previous thyroid illness, add up to 18 (26%) with altered thyroid function. From 61 patients who were tested for thyroid peroxidase antibodies, 22 (36%) were positive. Of 57 patients without a diagnosis of previous thyroid disease, in whom both the levels of serum thyrotropin and the presence of thyroid peroxidase antibodies had been studied, 24 (42%) presented at least one altered study. Given the high percentage of thyroid alterations in our series of patients, it seems clinically relevant to study the thyroid function and the presence of thyroid peroxidase antibodies in patients with chronic urticaria.