Clinical data: a 66-year-old woman referred for an evaluation of a rapidly enlarging bilateral thyroid mass. The tumor had evolved over 1.5 month.

Palpation: both thyroids were very hard, not freely moveable.

Functional state: hypothyroidism (TSH-level 21.0 mIU/L, FT4 6.09 pM/L, aTPO > 1000 U/L).

Ultrasonography: both thyroids were extremely enlarged, the dimensions of the right lobe was 75x55x120 mm. The whole thyroid was severely hypoechogenic, inhomogeneous. The vascularization was irregularly increased.

Cytological picture: corresponded to Hashimoto's thyroiditis with a greater ratio of lymphoblasts to small lymphocytes than in usual cases of thyroiditis.

Final combined clinical-ultrasound-cytological diagnosis: suspicion of a MALT-type lymphoma.

Biopsy and histopathology: MALT-type lymphoma of the thyroid.

Comment: the clinical presentation and patient history are the essence of the diagnosis of a MALT lymphoma of the thyroid. The primary role of cytology in such cases is the exclusion of an anaplastic carcinoma.