In order to determine whether permanent echo abnormalities are produced by subacute thyroiditis, ultrasound examination of the thyroid was performed repeatedly after a mean interval of 23 months in 17 subjects (8 women and 9 men) aged 31-52 (mean 41) years, suffering from subacute thyroiditis. The diagnosis was based on typical clinical symptoms, and cytological confirmation was obtained in all subjects but one. In the primary phase the ultrasonic finding was in all cases abnormal, showing either diffuse or focal hypoechogenicity and enlargement of thyroid lobes. At follow-up, a homogenous echo structure was found in 15 patients. Nodularity was detected in only two subjects. It is concluded that permanent focal echo abnormalities are generally not produced by subacute thyroiditis. Consequently, thyroid nodules in subjects with a history of SAT should not be ignored.