Patients with inflammatory arthritis and malignancy comprise two distinct populations. One group represents the chance occurrence of malignancy and rheumatic disease. These patients have symmetric polyarthritis, chiefly classic rheumatoid arthritis, and react positively to the rheumatoid factor test. There is no temporal relationship between tumor onset and rheumatic disease onset. In the second group, there may be a causal relationship between the malignancy and the rheumatic disease. These patients have asymmetric rather than symmetric arthritis and test results are negative for rheumatoid factor. There is a close temporal relationship between the onset of the tumor and the onset of the rheumatic disease. The mortality rate is significantly higher than in patients with symmetric polyarthritis. In 80 percent of women with asymmetric arthritis and malignancy, the tumor is mammary carcinoma. This indicates the advisability of a careful breast examination in this group of women.