Papillary thyroid carcinoma is one of the differentiated cancers of the thyroid. Hypothyroidism occuring after total thyroidectomy and ablative dose of radioactive iodine should be treated with L-thyroxine to prevent clinical symptoms and signs of hypothyroidism and occasional tumor growth. A 50-year-old female patient with a history of total thyroidectomy 15 years ago due to papillary thyroid carcinoma with capsule invasion followed by ablative dose of radioactive iodine and received no hormone replacement treatment from then-on since she was lost to follow-up was admitted with dyspnea on excursion and chest pain. Although she had laboratory findings of hypothyroidism, there was no remarkable clinical sign or symptom related to hypothyroidism other than isolated pericardial effusion. Her thyroglobulin (Tg) level was low but a halo image was observed in the pericardiac region with no other activity in the rest of the body in I131 scan. Differential diagnosis indicated that isolated pericardial effusion was due to hypothyroidism rather than recurrence of the papillary thyroid carcinoma. The importance of thyroid status evaluation in suspected individuals for the differential diagnosis of complications due to the recurrence of the underlying thyroid cancer or hypothyroidism and the reliability of Tg to rule out metastasis in cases with a false positive I131 scan are discussed on behalf of our case in the view of the literature.