Six cases are reported of an unusual synchronous association between aerodigestive squamous cell carcinoma and papillary carcinoma of the thyroid. Six males (47-62 years) were observed until 1975 at the Department of Head and Neck Surgical Oncology of the Istituto Nazionale Tumori, Milan. All were affected by aerodigestive cancer: oral cavity (1), pyriform sinuses (1), larynx (2), lip (1) and oropharynx (1). Clinical examination of the thyroid was always negative. For this reason they underwent surgery, complete surgical approach to aerodigestive neoplasm; one hemithyroidectomy and one total thyroidectomy were also performed. Unexpectedly pathological examination of the dissected lymph nodes indicated the presence of metastases of papillary carcinoma of the thyroid. Three of the six cases had only metastases of thyroid papillary carcinoma while the others presented both squamous cell and papillary carcinoma metastases. Excluding the 2 patients who had undergone thyroid surgery during aerodigestive cancer therapy, in 3 of the 6 patients, two total thyroidectomies and one hemithyroidectomy were performed after the metastases were discovered. In all cases, primary thyroid cancers were demonstrated. One patient did not undergo any subsequent surgery on the thyroid gland because of negative thyroid scanning and bad prognosis due to aerodigestive cancer. Two of the 6 patients died of aerodigestive cancer at 54 and 34 months, 2 are still alive and free of both diseases while one was lost after a 43 month follow-up.