All the patients committed in our laboratory for thyroid investigation underwent systematically a cervical echotomography. In a number of cases we stated a diffused microechoic character of the thyroid parenchyma. This character is present in most cases of Graves' disease, in a few cases of subacute thyroiditis spread to the whole gland and in chronic lymphocytic thyroiditis (LCT). 48 cases are reported here in which the microechoic character was evident and for which the diagnosis of Graves' disease or subacute thyroiditis were easily eliminated by biological and clinical arguments. In 31 cases, the diagnosis of LCT was clinically and biologically proved specially by significant levels of antithyroid antibodies. In the 17 other cases, the diagnosis of LCT was the most probably in spite of non sufficiently autoimmune proof. The diffused microechoic character of the thyroid parenchyma, even though it is non specific, appears thus a valuable sign in the diagnosis of chronic lymphocytic thyroiditis.