Pyriform sinus fistula is a rare anomaly arising from 3rd or 4th branchial apparatus and has been recognized as one cause of acute suppurative thyroiditis or acute deep neck infection. Pyriform sinus fistula must be considered when a clinician is encountered recurrent left lower neck abscess and a history of repeated incision and drainage. The confirmation of the diagnosis is made when the fistula tract is identified on a barium swallow study and when the internal orifice of the fistula is found at the apex of pyriform sinus on laryngoscopic examination. A complete excision of the fistula tract has been proposed as a treatment of choice. However, in some cases it is very difficult to resect the tract completely because of severe inflammation and repeated drainage procedure. We present three cases of pyriform sinus fistula which are successfully treated by laryngomicroscopic chemocauterization using synthetic fibrin and $AgNO_3$.