Sjögren's syndrome is an important autoimmune disease in the head and neck. Patients have an increased arrival risk of up to 6% per year for developing B-cell lymphomas, including mucosa-associated lymphoid tissue (MALT) lymphomas. The following case report shows this relation and the difficulty of differentiating clinically recurrent swelling of the parotid gland in Sjögren's syndrome from malignant lymphoma. A 64-year-old woman had a 2-year history of indolent, recurrent swelling of both parotid glands. Blood examination showed elevated ESR and a hypergammaglobulinemia. Immunosuppressive therapy produced no improvement. Two years after the diagnosis of Sjögren's syndrome, swelling of the left parotid gland persisted. Superficial parotidectomy of the left side was performed and histopathological examination revealed a MALT-related lymphoma. Subsequent parotidectomy of the right side also showed infiltration of the gland by a MALT lymphoma. Postoperative radiation therapy was given. During the follow-up period no recurrence or systemic disease was detected. Patients with Sjögren's syndrome should be examined regularly by the otolaryngologist. If a lymphoma cannot be ruled out, open biopsy must be considered for histological diagnosis. Prognostic factors for developing a lymphoma are possibly a high ESR and hypergammaglobulinemia. Further prognostic factors have to be evaluated.