Lemierre's syndrome is a rare, potentially severe disease consisting of septic emboli from an internal jugular vein thrombus after oropharyngeal infection. We report a 20-year-old man who had a tonsillitis with fever for 3 days. After a 2-day defervescence, fever relapsed as well as painful swelling over the left side of the neck. Computed tomography scan and sonography of the neck revealed thrombosis of left internal jugular vein and swelling of surrounding soft tissue. Chest radiograph demonstrated cavitary infiltrates over the left upper lobe. Septic thrombophlebitis of the internal jugular vein and metastatic pulmonary emboli was highly suspected. Intravenous ceftriaxone and metronidazole were given empirically. Fusobacterium necrophorum was isolated from the blood culture with susceptibility to metronidazole. Complete defervescence and resolution of the neck swelling and pulmonary infiltrates occurred after antibiotic administration for 21 days. Lemierre's syndrome should be considered when encountering a febrile patient with painful neck swelling.