A 40-YEAR-OLD otherwise-healthy white man presented with a 14-year history of a painless mass in the left side of his neck. He denied dysphagia, odynophagia, weight changes, voice changes, fever, chills, nausea, and vomiting. He did not smoke cigarettes or drink alcohol. Physical examination revealed no abnormalities except for a 6ϫ5-cm nontender, firm, mobile mass that was palpable in the left posterior triangle of the neck.The findings of fine-needle aspiration biopsy were nondiagnostic. A chest x-ray film was normal. A computed tomographic scan revealed a large enhancing mass in the left posterior cervical space (Figure 1). The wellencapsulated mass was subsequently excised in the operating room through a transverse incision in the posterior triangle of the neck. The histological findings are shown in Figure 2 and Figure 3.