It is well known that some patients with Sjögren's syndrome develop lymphoproliferative disorders. Approximately 60 cases of Sjögren's syndrome associated with malignant lymphoma, predominantly of B cell origin, have been reported in Japan. On the other hand, fourteen cases of non lymphoid malignant neoplasm, including six of thyroid cancer and four of gastric cancer, have been recently presented in Japanese literature. However, cases of double malignant neoplasms in Sjögren's syndrome are very rare. We reported a case of Sjögren's syndrome associated with breast cancer and B cell malignant lymphoma in the paper. A 53-year-old female was seen with eye pain, xerostomia, finger pain and right parotid swelling in January, 1985. Keratoconjunctivitis sicca was found. She had had eye pain and Raynaud's symptom during the past seven years. Sialectasia of grade III by Rubin and Holtz was seen in sialography. Schirmer's test was positive. Pathological finding of sialadenitis in minor salivary gland confirmed diagnosis of Sjögren's syndrome. Laboratory findings showed leukocytopenia and polyclonal hypergammaglobulinemia. Rheumatoid factor and antinuclear antibodies including SS-A antibodies were positive. Tuberculin test was negative. Ratio of CD 4 per CD 8 T lymphocytes was increased in peripheral blood. She had history of breast cancer. Radical mastectomy, followed by irradiation was performed in 1980. Arthralgia and parotid enlargement were transiently diminished by administration of small amount of prednisolone. She was readmitted because of progressive bilateral parotid swelling in April 1988. Pathological finding of the parotid was consistent with malignant lymphoma of diffuse, small cell type (lymphoplasmacytic). Immunoperoxidase staining revealed positive cytoplasmic IgM, k in lymphoma cells.(ABSTRACT TRUNCATED AT 250 WORDS)