Six hundred eighty-one consecutive patients with rheumatoid arthritis were followed for an average of 11.9 years to identify initial factors that predicted subsequent disability. Of 39 potentially predictive variables obtained at study onset and studied by stepwise regression methods, age was found to be the most powerful single predictor of disability, followed by radiologic grade, sex, and initial functional class. The worst prognosis for disability was found in patients who were older women and who showed radiologic worsening and developed functional impairment early in the disease course. Both disability and radiologic progression of disease were found to develop most rapidly during the first years after disease onset and to assume a slow, nearly linear rate of increase after 10 years. Approximately 10% of patients did not develop significant disability. This study suggests that it is possible to identify, early in the disease course, those patients who are likely to develop severe disability, and that "disease-modifying" therapy might well be initiated earlier in such patients and used consistently throughout the subsequent treatment.