Serum ferritin, one of the nonspecific tumor markers, was studied in 102 thyroid cancer patients, who had been thyroidectomized and were off thyroxine for 1 month, making them hypothyroid. Serum ferritin in thyroid cancer patients was not significantly different as compared to controls. Nevertheless, high levels of serum ferritin were observed in the thyroid cancer group as compared to primary hypothyroid patients. Furthermore, there was a significant difference in serum ferritin between thyroid cancer patients without metastasis and those with metastasis, patients with metastasis showing higher levels. Classification of thyroid cancer patients into different histological types revealed higher ferritin levels in follicular carcinoma as compared to papillary carcinoma. These data suggest that, although serum ferritin may not be a tumor marker for thyroid cancer, this parameter seems to be sensitive to the presence of metastasis and the histologic diagnosis.