A nontender goiter rapidly developed in a 54-year-old patient with suspected disseminated carcinoma. Thyroid function tests showed increased thyroxine, triiodothyronine resin uptake, free thyroxine index, and free thyroxine. Radioactive iodine uptake by the gland was near zero, and thyroid-stimulating hormone (TSH) was undetectable. Histologic examination of the thyroid before and after death showed invasion and disruption of the thyroid follicles by adenocarcinoma (pancreatic primary). Release of thyroglobulin by follicular disruption probably resulted in hyperthyroxinemia and suppression of TSH and radioactive iodine uptake, as occurs in subacute thyroiditis.