Preoperative diagnosis of the presence of anomalies or abnormalities of the cervical vessels is important to safely perform neck dissection in patients with head and neck cancer. We present a case of cervical lymph node metastasis from carcinoma of unknown primary origin in a 72-year-old man. The patient had a huge lymph node metastasis in his right neck that was more than 90° adjacent to the common carotid artery. Imaging studies incidentally revealed right internal carotid artery hypoplasia. Internal carotid artery hypoplasia is a very rare vascular anomaly with an incidence of