Clinical data: a 71-year-old woman was referred for an evaluation of a hard painless mass discovered by the patient herself three months earlier.

Palpation: a very hard nodule in the right lobe.

Functional state: euthyroidism (TSH-level 1.01 mIU/L).

Ultrasonography : there was a large hypoechogenic nodule with irregular surface in the right thyroid. The vascularization was decreased.

Cytology: suspicion of a small cell malignant tumor. Immunocytochemistry was not successful.

We performed lung-CT with negative result.

Biopsy was performed from the right thyroid and histopathology revealed large B cell lymphoma.

Comment: in our practice with malignant lymphomas of the thyroid the immunocytochemistry was not successful in around 50% of cases, while in another 25% of cases was not fully diagnostic.