Warthin tumor is a benign salivary gland tumor which usually occurs in the parotid gland, but rarely in the cervical lymph node. We report a Warthin tumor in a contralateral parotid gland lymph node that mimicked metastasis of oral floor cancer on FDG-positron emission tomography/computed tomography （PET/CT）. For treatment of oral floor cancer, a man in his 70s was referred to our department. CT showed a 14×11×9mm mass below the contralateral parotid gland. FDG-PET/CT showed abnormal accumulation （SUVmax＝4.7） of FDG in the mass. Because differential diagnosis of lymph node metastasis and Warthin tumor was difficult, CT lymphography （CTL） was performed. Although CTL revealed one sentinel lymph node in the right submandibular region, there was no lymphatic flow to the contralateral parotid lymph node. Therefore, the patient underwent tumor resection and biopsy of both lymph nodes. The pathological diagnosis of the contralateral parotid lymph node was Warthin tumor. There was no evidence of recurrence and metastasis 11 months after surgery.