Objective: To investigate the clinicopathologic features, diagnosis and differential diagnosis of primary thyroid lymphoma (PTL). Methods: The clinicopathologic data of 25 cases of PTL collected in Shanghai General Hospital from 2009 to 2018 were analyzed retrospectively. Microscopic examination and immunohistochemistry were performed for studying its pathologic characteristics and immunophenotyping. Results: Totally 25 cases were diagnosed with PTL by pathologic examination after a surgical operation, including 10 males and 15 females whose average age was 56.3 years. A total of 19 (76.0%) patients had a clinical history with Hashimoto’s thyroiditis (HT), and 12 (66.7%) cases were positive for hepatitis B virus infection. Totally 25 cases were diagnosed with B cell lymphomas, including diffuse large B-cell lymphoma (DLBCL, 15 cases), marginal zone B-cell lymphoma of mucosa-associated lymphoma tissue (MALT, 8 cases), marginal zone B-cell lymphoma of MALT-type with large cell transformation (mixed DLBCL and MZBL, 2 cases). Morphologic features of PTL characterised the destruction of thyroid structure. Tumor cells immunohistochemically express cluster of differentiation 20 (CD20) which was a marker of B cell lymphoma. Conclusion: PTL mostly affects middle aged and old female with HT, and its main histologic type is non-Hodgkin B cell lymphoma. PTL should be differentiated from thyroiditis, thyroid undifferentiated carcinoma and medullary carcinoma etc. Different vary greatly in pathologic features, growth pattern and prognosis, so the determination of pathological types of the tumor at diagnosis is critical for clinic follow-up and treatment.