A 19-year-old male patient presented with lymphocytic interstitial pneumonia and Sjögren's syndrome, confirmed by histopathology. He was treated with prednisone; 4 months later, cyclophosphamide was added. A lymph node taken at presentation revealed no histological signs of malignancy. Lymph nodes obtained 1 and 2 years later exhibited an effaced structure and a diffuse infiltration of small-sized lymphocytic cells compatible with a low-grade non-Hodgkin's lymphoma. The immunological phenotype of the lymphoma resembled that of immature T-cells present in the normal thymus cortex--positivity for CD1, CD2, CD4, CD7, CD38 and terminal deoxynucleotidyl transferase; faint positivity for CD5 and in the second specimen for CD3; negativity for CD6 and MHC class 1 antigen. The occurrence of such a peculiar lymphoma in Sjögren's syndrome has not been reported thus far. Small numbers of putative malignant cells were found on immunohistochemistry in a lymph node and a lung biopsy obtained at presentation. This is suggestive of one underlying pathogenetic event in the development of lymphocytic interstitial pneumonia, Sjögren's syndrome and non-Hodgkin's lymphoma.