OBJECTIVE This study aims to investigate the pathogenesis, clinical characteristics, diagnosis, treatment, and prognosis of primary thyroid lymphoma (PTL) for a better understanding of the disease and a more accurate PTL diagnosis, thereby preventing misdiagnosis and mistreatment. METHODS The clinical manifestations, biochemical examination, ultrasound examination, imaging examination, pathologic examination, diagnosis, and treatment of four PLT patients admitted to the Department of Thyroid and Breast Surgery of the Affiliated Hospital of Inner Mongolia Medical University from January 2010 to December 2020 were retrospectively analyzed. RESULTS Diffuse large B-cell lymphoma (DLBCL) expressing cluster of differentiation 20 (CD20) were detected in all four PTL patients. Hashimoto's thyroiditis (HT) with increased anti-thyroglobulin antibodies (TGAb) occurred in two PTL patients, while antithyroid peroxidase autoantibody (TPOAb) was increased in three cases. All four patients underwent surgical and chemoradiotherapy treatments. Patients were without tumors during the follow-up ranging from 8 to 55 months. CONCLUSIONS PTL is a primary extranodal lymphoma of the thyroid and is mainly derived from B-cell non-Hodgkin's lymphoma. The pathogenesis of PTL remains unclear, but it is closely related to HT. Clinical diagnosis in this study was determined by either needle biopsy or surgical resection.