Clinical presentation: a 36-year-old woman was presented with a rapidly growing mass in the right thyroid. The lesion had evolved over 3 months.

Palpation: the right thyroid greatly, the left moderately enlarged. Both lobes were stone-hard and painless.

Functional state: subclinical hypothyroidism (TSH-level 8.93 mIU/L, FT4 11.2 pM/L).

Ultrasonography: the whole thyroid was hypoechogenic. The extent of hypoechogenicity almost reached that observed in cystic lesions. No vascularization was detected.

Cytological picture: repeatedly not diagnostic.

Histopathology: Riedel thyroiditis.