Objective: Suppurative acute thyroiditis is caused by pyriform sinus fistula (PSF), and PSF frequently elicits deep neck abscess. However, complete fistulectomy is the ideal management of PSF, and studies on surgical findings of PSF are exceedingly rare. This study aimed to reveal the origins of PSF, each route, and clinical presentation. Methods: This is a multicenter study. We have conducted 19 complete fistulectomies of PSF in Japan, analyzed routes of the fistulas, estimated the origins, and investigated their histological and clinical findings. Results: No recurrence was observed in all cases. Five of 12 cases showed thymic and/or parathyroid tissues around the fistulas, passing inside the inferior horn of thyroid cartilage, were regarded as having 3rd pouch origin, and tended to have low frequency of severe deep neck abscess. The remaining seven cases originated from the 4th pouch running outside of the horn and showed frequent severe infection. Conclusion: PSF have two different routes depending on their generation and may present different clinical manifestations.