Primary biliary cirrhosis is characterized by abnormalities in both cellular and humoral immunity. It is associated with presumably autoimmune diseases such as Sjögren's syndrome, rheumatoid arthritis, and scleroderma. Sjögren's syndrome and scleroderma have been noted to have an increased frequency of malignancy. Of 208 patients with primary biliary cirrhosis, followed for one month to 15.9 years, extrahepatic malignancies developed in 11, six of whom were women with breast cancer, and one with hepatocellular carcinoma. The incidence of breast cancer was 4.4 times (p less than 0.01) the incidence expected from the rate prevailing in the same age range in a comparable normal population. The incidence of cancer in sites other than the breast and of primary hepatocellular tumor was not significantly increased.