Metastatic thyroid tumor is rarely diagnosed clinically. We report here a case of a 59-year-old male of a primary squamous cell carcinoma of the lung with metastatic thyroid tumor diagnosed by an ultrasonography-guided aspiration cytology. A squamous cell carcinoma of the lung (c-T4N3M1 stage IV) was diagnosed in March 2001, and so chemotherapy using carboplatin and paclitaxel was tried initially. A partial response was obtained. Then, he was re-admitted to our hospital because his thyroid gland was swollen. Ultrasonography-guided aspiration cytology of the thyroid tumor was performed and revealed a metastatic squamous cell carcinoma from the lung cancer. The patient was given chemotherapy using gemcitabine and docetaxel as second line chemotherapy. This reduced the thyroid tumor size and improved the symptoms.