Measuring tumor marker levels following cancer treatment can be useful. Although serum thyroglobulin is a useful marker after total thyroidectomy for papillary thyroid carcinoma (PTC), it is not a reliable marker for patients with a high titer of anti-thyroglobulin antibodies or when transformation to undifferentiated carcinoma has occurred. The female patient in this case report underwent total thyroidectomy and oral I-131 therapy for PTC at the age of 47 years, followed by cervical lymph node and lung resections for metastases, 3 and 11 years later, respectively. She also received oral I-131 therapy and external beam radiotherapy for mediastinal lymph node metastases. The lymphadenopathy lesions progressed and multiple lung metastases were detected when she was 61 years of age. She died at the age of 62 years. The serum CA19-9 level had gradually increased in association with enlargement of the recurrent lesions and immunostaining of CA19-9 in the pulmonary metastasis was intense. Thus, we consider that measuring the level of serum CA19-9 is an effective tool for evaluating disease status after surgery for PTC.