BACKGROUND Intravascular large B-cell lymphoma (IVLBCL) is a subtype of diffuse large B-cell lymphoma (DLBCL) that is rare and highly aggressive and that may progressively involve many organs. CNS (central nervous system), BM (bone marrow) and skin are the most common systems involved. To date, only 2 cases of IVLBCL involving the thyroid have been reported. METHODS Here, we report a case of IVLBCL involving the thyroid and accompanied by bilateral nodular goiter. In this case, a thyroid mass was identified in a physical examination of a 68-year-old male who initially presented with dyspnea accompanied by intermittent headache for approximately 1 month. Computed tomography scans revealed that the left lobar thyroid was occupied by a large, slightly lower density mass (5.8 × 4.7 × 8.4 cm). However, the patient had no hyperthyroidism or hoarseness. Levels of thyroid hormones and anti-thyroid autoantibodies in the serum were normal preoperatively. Thyroid mass resection was performed to establish a diagnosis and to relieve symptoms. CONCLUSIONS Pathological results of the surgical specimen revealed that large atypical lymphoma cells filled the capillaries in the lesion area. Immunohistochemical staining revealed that the large-sized tumor cells were positive for CD20, PAX-5, MUM-1 and BCL-2, and were negative for CD3, CD5, CD43, CD10, CD23, CyclinD1, CD138, CD30, ALK, CD56, MPO, S-100, TTF-1, TG (thyroglobulin) and CT (calcitonin). The Ki-67 index was estimated to be approximately 85%. The patient was subsequently diagnosed as "Classical" IVLBCL non-germinal center B-cell type. The patient declined chemotherapy and died in the fifth month after operation.