Acute suppurative thyroiditis is an uncommon thyroid disorder usually caused by bacterial infection. The most common route of infection is a fistula that originates from the fundus of the pyriform sinus. Pre-existing thyroid disease, most commonly nodular goiter, has been reported to be present in acute suppurative thyroiditis. A 44 year old man presented a subacute thyroiditis, resolved by nonsteroidal antiinflammatory treatment. One year later, the patient abruptly complained of fever and painful swelling in the thyroid region. A relapse subacute thyroiditis was diagnosed and prednisone treatment was started. A few days later owing to a worsening of the pain and of the clinical features the patient was referred to our department. He presented dysphagia and he was feverish, the overlying skin of the neck swelling was erythematous and warm. There was a neutrophilia (83.7%). Plasma FT4, FT3 and TSH were normal. Anterior neck region ultrasonography showed an enlargement of the left thyroid lobe with poorly defined shapes and inhomogeneous parenchyma while the right lobe of the gland was normal. The 131-I thyroid scan showed a large cold area in the upper part of the left thyroid lobe and preserved radionuclide uptake in the residual parenchyma. The RAIU was normal. We diagnosed acute suppurative thyroiditis and started antibiotics treatment. The day after the patient was still feverish and he gave out from the mouth a great quantity of sero-purulent material with a swelling reduction and improvement of the neck pain. Barium swallow examination did not show any fistula in the cervical esophagus. The fistula opening was demonstrated by indirect laryngoscopy in the postero-lateral side of hypopharynx.(ABSTRACT TRUNCATED AT 250 WORDS)