A 43-year-old woman presented to the endocrinologist with symptoms and signs of typical thyrotoxicosis caused by Graves' disease. Review of systems revealed that she had recently discovered a lump in her left breast. Evaluation of the left breast lesion led to a core biopsy that showed sclerosing lymphocytic lobulitis. This breast disease, well recognized in the pathology literature, occurs in various autoimmine disorders, particularly type 1 diabetes mellitus, and has occasionally been reported in Hashimoto's thyroiditis. The patient described here represents the first published association of sclerosing lymphocytic lobulitis of the breast with Graves' disease.