RESUMEN
Hashimotos thyroiditis and Graves disease have been thought to be the autoirnmune diseases having their distinct and separate clinical and pathologic features. Because of the partial and complete simi1arity in histologic feature, it has been hypothesized that Hashimoto's thyroiditis and Oraves disease may be interrelated. Several patients who had been diagnosed as Graves disease showed features of hypothyroidism, and were proven to have histologie features of Hashimotos thyroiditis in their thyroid tissue. Two meehanisms had been suggested to explain tbis phenomenon. One is that the combined Hashimotos thyroiditis in Graves' disease may become predominant with time, The other is that the amount of TSH receptor blocking antibody may increase in the course of Graves disease. Early recognition of these patients would be impartant to estabilish therapeutic plan. Futhermcee, extensive study of these patients would give more understanding of the mechanism of these diseases. Here we report 5 cases of clinically diagnosed Graves disease with pathologic features of Hashimotos thyroiditis or focal lymphocytic thyroiditis.