AbstractFifteen patients with subacute thyroiditis were studied with thyroid sonography. There were local hypoechoic areas in all patients during the active phase of the disease. Among 6 patients who underwent follow‐up studies during the course of treatment, 3 had recurrence or aggravation of clinical symptoms such as painful swelling of the thyroid region, which was associated with, and sometimes preceded by, spread or reappearance of the sonographic abnormality. All 6 patients showed complete disappearance of the hypoechoic area when they were in remission. The thyroid sonography is useful not only for the initial diagnosis but also for the follow‐up of these patients during the course of the dise