CD45, also referred to as the leukocyte common antigen (LCA), is selectively expressed on nucleated hematopoietic cells in healthy individuals. It is also widely expressed in various types of hematologic malignancies--although 10% of acute lymphoblastic leukemia and more than 50% of multiple myeloma have been reported to lack its expression. In this paper, we report a rare case of CD45-negative non-Hodgkin's lymphoma (NHL) that affected the thyroid gland.