We report on two new patients with both rheumatoid arthritis and multiple sclerosis. In one patient, the first manifestations of multiple sclerosis occurred eight years after onset of seronegative rheumatoid arthritis without extraarticular manifestations. The other patient had a 20-year history of multiple sclerosis when she developed seropositive, nodular rheumatoid arthritis. Neither patient had evidence of systemic lupus erythematosus. A lip biopsy was done in one patient, with normal results; the other patient was free of clinical symptoms of sicca syndrome and had a negative Schirmer's test. The paucity of similar cases in the literature is surprising since multiple sclerosis and rheumatoid arthritis are both autoimmune diseases and share many pathophysiologic and etiologic features. Although chance alone may explain the occurrence of both conditions in the same patient, the existence of shared etiologic factors should in theory increase the likelihood of the association.