Six patients with thyroid cancer presented with clinical and, in most cases, biochemical features of subacute or chronic thyroiditis. Pathologic study revealed all types of cancer, including metastatic and neighborhood parathyroid malignancy. Confusion in diagnosis lead to a delay of diagnosis of one month to ten years. When thyroiditis is diagnosed, the patient should be followed carefully, including the use of needle aspiration biopsy. Where doubt exists as to diagnosis or response to treatment, open biopsy or operation may be indicated.