Primary thyroid lymphoma (PTL) is an exceptionally rare and highly aggressive potentially curable malignant disease. We report three typical cases of PTL referred to our hospital. All three cases had long history of Hashimoto's thyroiditis, and presented with progressively enlarging neck mass. The first two cases were confirmed by surgical biopsy to be diffuse large B cell lymphoma, and received radiotherapy combined with chemotherapy, or received only chemotherapy. The third case was confirmed by core needle biopsy to be mucosa-associated lymphoid tissue lymphoma, and received radiotherapy. In summary, confirmation of PTL diagnosis is essential for further clinical decisions. Core biopsy should be one of the most important methods to make the diagnosis of PTL, while the use of fine needle aspiration cytology alone is still limited in diagnosing PTL.