Acute suppurative thyroiditis is an infection originating from the piriform sinus via a congenital fistula. Between April 1987 and April 2002, we treated five patients with piriform sinus fistula with acute suppurative thyroiditis, three boys and two girls with ages ranging from 4 to 16 years. The diagnosis of piriform sinus fistula was made by hypopharyngeal enhancement radiography in all five patients preoperatively. Surgical treatment was performed after reduction of inflammation. Total fistulectomy including partial thyroidectomy was performed in three patients, and partial fistulectomy via piriform sinus to thyroid was performed in the other two patients. Administration of 1% methylrosarilinium chloride orally before the operation clearly distinguished the fistula from the surrounding tissue without any difficulty in the operative field. No inflammatory recurrence was observed in any patient during the follow-up period.