We report a 42-year-old female patient with sclerosing inflammatory pseudotumor. She had found a mass in her left neck after she caught a cold. An elastic hard mass (25 x 15 mm), unaccompanied by any other symptoms, was palpated adjacent to the left carotid bifurcation. The mass extended vertically along the common carotid artery, partially adhering to the pulsating artery. Under ultrasonography, the mass was characterized by a homogenized low echoic shadow surrounding the left common carotid artery. Angiography revealed a slight narrowing of the common carotid artery with a surrounding hypovascular mass. Computerized tomography (CT) and magnetic resonance imaging (MRI) both showed a mass enclosing the carotid artery; a Ga scintigram also showed a highly concentrated mass. Surgical removal of the mass included removing part of the carotid artery, internal and external carotid arteries and sympathetic trunk. The left internal jugular vein was transplanted to connect the common carotid artery to the internal carotid artery. Although the hypoglossal and vagus nerves adhered to the mass, they were preserved by sharp dissection with the scalpel. Although hypoglossal and vagus nerve dysfunction were observed temporarily after the surgery, Horner's syndrome appeared and persisted. Histological examination revealed markedly fibrotic tissues surrounding the carotid artery with extensive lymphocyte and plasmacyte infiltration and a diagnosis of sclerosing inflammatory pseudotumor was made.