Background: The coexistence of granuloma annulare (GA) and autoimmune thyroiditis (AT) has been sporadically observed in female patients, but the significance of this rarely reported association remains uncertain. Objective: To investigate for the first time the frequency and type of thyroid disease in adult women with localized granuloma annulare (LGA) compared with a matched control group. Methods: Twenty-four adult women with histology-proven LGA and a control group of 100 age-matched female patients with other unrelated cutaneous diseases were screened for thyroid disease in a tertiary teaching hospital in northern Spain. Laboratory evaluation included routine hematologic and chemistry analysis, antinuclear antibody, rheumatoid factor, thyroid function test (sensitive thyroid-stimulating hormone [TSH]), thyroid autoantibody levels, and antibodies to thyroid peroxidase in all patients and controls. Thyroid hormones (free triiodothyroxine and free thyroxine) were measured when TSH value was abnormal. AT was defined as hypothyroidism (TSH value >5 mU/L) and in addition to elevated antithyroid antibodies or characteristic thyroid biopsy. The results were compared using Fisher's exact test. Results: Statistical evaluation of the findings obtained in this study showed mainly that the frequency of AT was increased significantly in the group of adult women with LGA (3/24, 12%) compared with the matched control group (1/100) (Fisher's exact test: P = .022). Conclusion: Although little can be inferred from a single investigation, the results of this pilot study indicate an association between LGA and AT in adult female patients, supporting the theory that at least a subset of GA belongs to the spectrum of autoimmune diseases. (J Am Acad Dermatol 2003;48:517-20.)