The objective of this paper was to find out how many patients with rheumatoid arthritis (RA) know about several aspects of disease, to explain the associations between the level of self-rated knowledge and patients' background and health status and to compare the importance of the main sources of information. A random sample (n = 1,259) of adult Estonian RA patients was selected from the Estonian Health Insurance Fund Database. The patients completed a self-administered questionnaire, which included information about their socio-demographic and disease characteristics, use of health services, information about the disease, and sources of information. Regression analysis was used to calculate the associations between the independent variables and level of self-rated knowledge about several aspects of RA. The results of the study indicated that the self-reported ratings of knowledge about the disease in Estonian RA patients were rather low. Health professionals were mentioned as the primary sources of information, but the longer disease history and more frequent use of health services as considerable predictors of higher ratings of knowledge refer to role of personal experience in obtaining knowledge about the disease as well.