The aim of this study was to assess the prevalence of malignant lymphomas in patients with long-standing primary Sjögren's syndrome (pSS). We retrospectively studied a cohort of 55 patients with pSS over a mean follow-up period of 12 years. Five patients (9%) developed malignant lymphoma. The interval between the diagnoses of SS and lymphoma ranged from four to 12 years (mean = 6.5 years). The lymphoma arose in the lymph nodes in two cases, the parotid gland in one case, the lacrimal gland in one case, and the lung in one case. All five cases were B-cell low-grade lymphomas. Among our SS patients, those with extraglandular manifestations and/or a mixed cryoglobulin were at increased risk for lymphoma development. Secondary lymphoma carried a poor prognosis in our study. Three of the six SS patients who died during the follow-up period had lymphoma.