An ectopic malignant thymoma in association with occult papillary adenocarcinoma in the thyroid, seen in a 58-year-old female, was reported. Clinically, this tumor took after a thyroid carcinoma. Thyroid scintigram using 99mTcO4- showed a cold nodule, while 201Tl radio-isotopes were markedly accumulated in the tumor lesion. Since the tumor invaded the left thyroid lobe and isthmus, recurrent nerve, trachea and esophageal muscle layer, subtotal thyroidectomy with resection of 2nd to 4th tracheal rings and partial resection of the esophageal muscle. The defective trachea was reconstructed by end to end anastomosis. Histologic examination revealed a malignant thymoma of mixed type and an occult papillary adenocarcinoma in the thyroid gland. Two year and three month follow-up showed no local recurrence and metastasis.
