Clinical presentation: a 42-year-old man was referred for an evaluation of hypothyroidism. He had got daily 15 mg (!) iodine for two years in order to loose weight.

Palpation: both thyroids were very firm, but no nodule was palpable.

Hormonal investigation: indicated severe hypothyroidism with TSH-level 140 mIU/L, FT4 < 3 pM/L.

Ultrasonography: revealed moderately hypoechogenic inhomogeneous thyroids. There was a hyperechogenic nodule in the lower part of the left lobe. It presented a halo sign and perinodular blood flow.

Cytology: was performed from the nodule and resulted in lymphocytic thyroiditis.

Anti-TPO: above 1000 U/mL.

Clinical diagnosis: autoimmune thyroiditis, hypothyroidism.

Follow-up investigation: 3 months later the biochemical parameters were unchanged despite of the ceasing of the iodine administration. Therefore, we started replacement therapy. One year later the patient was euthyroid on daily 150 microgram levothyroxine. The anti-TPO level at this time was already above 1000 U/mL.