This is a report for an unusual case of oxyphilic cell adenocarcinoma originating from anterior mediastinum in a 36-year-old male who complained of his neck lymphoadenopathy. 201Tl whole body scanning showed increased uptake of the left supraclavicular and upper mediastinal regions. There was no history of prior operation nor irradiation to the thyroid or neck region. Chest CT scanning also demonstrated the tumor in the superior mediastinum, but the mass has no increased 67Ga uptake. No tumor in the thyroid lobes was apparent on thyroid scintiscanning, ultrasonography and neck CT. The mediastinal tumor resection, the right and left thyroid lobectomy and the neck lymphonodectomy were completed. Serial sectioning of the resected thyroid lobes failed to show any tumorous tissue. The light microscopic features of a Hurthle-cell tumor arising in the mediastinal ectopic thyroid and diagnosed by neck lymph node biopsy were presented. The tumor was clinically malignant, having metastasized to the bone and the neck lymph nodes. Non surgical treatment including radioactive iodine (131I) therapy and combination chemotherapy were disappointing. The patient deteriorated progressively and died 16 months after thyroidectomy. We describe here an unusual case of a papillary growing and thyroglobulin producing tumor in the superior mediastinal region without evidence of a primary thyroid gland tumor.