Objective To investigate the clinical-pathological feature of careinoma showing thymus-like dif- ferentiation(CASTLE) of the thyroid. Methods The clinical data, histopathologie changes and immunohistoche- mical findings were studied in 1 case of carcinoma showing thymus-like differentiation of the thyroid with review of the related literature. Results The age of the patient was 38 years old. The clinical manifestation displayed a pain- less mass in the thyroid. On ultrasound the tumor appeared hypoechoic. Histologically the tumor cells were arranged in nests and islands accompanied by desmoplasfie strorna. The architecture thus showed a superficial resemblance to the lobulation seen in thymic carcinomas. The tumor was characterized by squamoid or syheytial-appearing cells with lightly eosinophilic cytoplasm. Nuciec were oval, pale to versicular, and had small distinct nudeoli. Immunohistoche- mically the tumor cells were positive for CK, CD5, CD117 but neyative for TG, Calcitonin, SYN, NSE, TTF- 1, EBV. Conclusion CASTLE is a very rate a carcinoma thyroid with architectural resemblance to thymic epithelial tumors. The immunophenolype of CASTLE is identical with that of thymie carcinoma.