Primary thyroid lymphoma (PTL) is a relatively rare disease, accounting for less than 0.5~5% of all thyroid malignancies. We encountered two cases of a primary thyroid lymphoma with Hashimoto's thyroiditis; one in a 63-year-old man and the other in a 79-year-old woman. The first case was a mucosa-associated lymphoid tissue lymphoma, and the other was a diffuse large B-cell lymphoma. Both patients underwent surgery and radiotherapy after being diagnosed using fine-needle aspiration cytology (FNAC). Both patients recovered well with no recurrence throughout the study period. The role of the surgeon in the treatment and diagnosis of thyroid lymphoma has been reduced due to the development of FNAC and combination therapy with chemotherapy and radiotherapy. On the other hand, surgery can be an effective treatment option for PTL confined to the thyroid, for achieving a definitive diagnosis, and in the treatment of patients with an airway obstruction.