Mucosa-associated lymphoid tissue lymphomas are a relatively recently recognized subset of B-cell non-Hodgkin's lymphomas. Generally, mucosa-associated lymphoid tissue lymphomas in the thyroid gland are known to have good prognosis, but recurrence and metastasis have also been reported.

A 70-year-old man visited our clinic with a 2-month history of a painless, rapidly growing mass in the neck associated with dysphagia. Left hemithyroidectomy was performed due to dysphagia. The histologic examination and immunohistochemistry showed an extranodal marginal B cell-type mucosa-associated lymphoid tissue lymphoma. He remains alive 57 months after the surgery.

If a diagnosis of a thyroid mass is unclear in a patient who exhibits symptoms of the neck, surgical treatment may be helpful for diagnosis and to relieve symptoms.