Thyroid sonography was used to assess 2322 patients attending our clinic over a 3-year period. Sonography, in combination with clinical and laboratory findings, enabled us to detect autoimmune thyroiditis in 123 patients, 67 of whom could be classified as euthyroid, 17 as latent hypothyroid, and 39 as overtly hypothyroid. Consequently without the use of sonography (or thyroid antibody measurements) it would not have been possible to make a diagnosis in over half of our patients with autoimmune thyroiditis. Sonography was also of considerable value in establishing the absence of autoimmune thyroiditis as out of the 2322 patients we examined, autoimmune thyroiditis could be excluded on the basis of sonography alone (absence of diffuse hypoechoicity) in 1962 (84%). Thyroid volume ranged from < 5 to 112 ml with the majority of patients having a volume of 21-30 ml and the overtly hypothyroid group showing a shift to smaller volumes. The data suggested that thyroid volume changes over the range of the disease from euthyroid to overtly hypothyroid.