Maltomas of the thyroid are rare neoplasms that originate from parafollicular B lymphocytes and are often associated with autoimmune thyroiditis (Hashimoto's disease). The authors describe a case of a primary thyroid lymphoma in which no evidence for a previous thyroiditis could be found during clinical evaluation (clinical progression of the tumor, diagnostic studies, preoperative cytology, histology of the surgical specimen). Noteworthy was the development of a severe form of pure red cell aplasia (PRCA) about 6 months after the operation without detectable autoantibodies or signs of previous viral infection. The aplasia resolved completely with corticosteroid therapy.