Internal jugular vein thrombosis (IJVT) is an elusive vascular disease that is rarely seen, with potentially lethal complications such as sepsis and pulmonary embolism. Spontaneous IJVT is considered when no apparent predisposing cause of thrombosis is present. Apreviously healthy, 31-year-old woman presented to the university-based emergency department because of painless swelling in the right anterior side of her neck. Physical examination revealed a painless, soft and immobile mass in the right anterior side of her neck beneath the sternocleidomastoid muscle, without hyperemia or local heat. On ultrasonographic examination, a hyperechogenic mass was visualized around the thoracic entrance of the right internal jugular vein, which was suggestive of a thrombus. The patient was administered intravenous antibiotic and low-molecular-weight heparin followed by oral coumadin as anticoagulant therapy. Her complaints were relieved within 5 days. She was completely well after 6 months. Venous thrombosis generally results from impaired blood flow locally or systemically that leads to activation of coagulation. Primary care physicians should sustain a high index of suspicion in patients who present with undiagnosed swelling in the neck, or other signs and symptoms attributed to IJVT.