BACKGROUND: Unilateral invasion of the internal jugular vein (IJV) after subtotal thyroidectomy caused by local recurrence of papillary thyroid carcinoma is extremely rare. We report a case of papillary thyroid carcinoma which invades IJV with hypervascular tumor thrombus. CASE REPORT: We report a case of a 52-year-old woman with a history of previous thyroid operation who presented with a 2-month history of a painless, growing, hard, solitary mass on the left side of the neck. Clinical examination revealed also ipsilateral cervical lymphadenopathy. Radiological examination showed a necrotic and cystic mass arising from the operated area extending and invading the left jugular vein wall with hypervascular tumor thrombus. Cytological examination of the mass confirmed a papillary thyroid carcinoma (PTC) and enlarged metastatic lymph nodes. Therefore, total thyroidectomy with left neck dissection and segmental resection of the left internal jugular vein were performed, and the tumor thrombus was cleared successfully. CONCLUSIONS: Invasion of IJV with hypervascular tumor thrombosis is an extremely rare condition in papillary thyroid carcinoma. Thrombosis of IJV is probably underdiagnosed. Early-stage diagnosis is important for long-term survival rates.