Malignant thymoma is usually manifested as a mediastinal mass. Occasiomally, these tumors may be associated with a variety of systemic syndromes, such as myasthenia gravis, pure red cell aplasia or hypogammaglobulinemia However, it is generally accepted that thymomas rarely metastasize and the frequency of extrathoracic metastasis has been reported as 1 to 15%. In general, nuclear changes of tumor cells such as enlarged size, irregular shape and altered textures are determining factors in the assessment of the grade of malignancy. We experienced a case of malignant thymoma of anterior mediastinum in a 35-year-old woman. After 3 years, she developed recurrent malignant thymoma in the right supraclavicular area, diagnosed by aspiration biopsy cytology.