The relationships between rheumatoid arthritis and malignant disease have been a focus of controversy for many years. The body of available data supports a relative decrease in the overall rate of occurrence of cancer, in particular of the colon, with no significant impact on mortality. However, increases have been demonstrated in the relative risks of lymphoma and, to a lesser degree, leukemia. The concomitant occurrence of rheumatoid arthritis and multiple myeloma seems fortuitous, with a relative risk of approximately 2. The effect of treatments, including methotrexate, remains unproven to date.