Lymphocytic infiltration of the thyroid gland is the pathologic hallmark of autoimmune thyroid disease. Lymphoid cells are seen in the stroma of glands affected by Graves' disease. However, large lymphoid infiltrates are characteristic of that spectrum of diseases conveniently termed chronic lymphocytic thyroiditis. In this review, the pathology of the various subtypes of chronic thyroiditis is enumerated, including recently defined lesions, i.e., painless thyroiditis, thyroiditis associated with interleukin chemotherapy, and peritumor thyroiditis are reviewed. The unifying morphologic characteristics seen in these conditions are discussed.