This article presents a case of Behcet's Disease (BD) with vascular involvement of the neck, which mimicks a metastatic neck mass in the initial presentation. A 58-year-old man presented with dysphagia, weight loss, bulging on the lateral, wall of the left pyriform sinus, and a firm and fixated neck mass suggestive of metastasis. Computed tomography of the neck demonstrated a solid mass, around the bifurcation of the carotid artery together with a pseudoaneurysm of the left external carotid artery. The mass was about four centimeters in diameter and extended to hypopharynx medially. Biopsy from neck mass and hypopharynx revealed no specific pathology. During follow-up the firm and fixated mass changed into a completely pulsatile one in the following three weeks. Reassessment of the patient's past history in detail revealed that he had had recurrent oro-genital ulcers, arthralgia and recurrent skin lesions. The pathergy test was positive. The patient was diagnosed to be BD and treatment consisting of colchicine 1 mg/day, peroral was started. He had a favorable outcome after treatment and was asymptomatic at follow-up of 24 months. It is unusual for BD to present as a neck mass but yet it must be considered in the differential diagnosis of neck masses. The present case report demonstrates how such a mass may mimic metastatic tumoral involvement and cause diagnostic dilemma. (c) 2005 Tohoku University Medical Press.