Rheumatoid arthritis is a chronic inflammatory disease leading to disability, reduced quality of life, and severe depressive symptoms. Theoretical models and research emphasize the importance of cognitive factors such as illness-related beliefs and cognitive appraisals in the process of adapting to life with a chronic disease. Objectives: The aim of this study was to analyze the role of age, disease duration, and cognitive factors in the level of acceptance of life with rheumatoid arthritis and determine the factors responsible for short-term (one week) changes without the use of interventions. We also assessed differences in predictors between rheumatoid arthritis, vascular diseases, and diabetes. Methods: Data were collected using a panel study. The first part of the analysis included 83 participants who declared a medical diagnosis of rheumatoid arthritis. In the second part of the analysis, in addition to people with rheumatoid arthritis (69 participants), two control groups were also included: diabetes (n = 26) and vascular disease (n = 26). The analysis examined basic sociodemographic and clinical data, cognitive appraisals, illness-related beliefs, and acceptance of living with the disease twice in one week. Results: The relationship between age and levels of acceptance of living with the disease was cubic, but the groups distinguished based on age and disease duration did not differ in terms of the analyzed variables. Cognitive appraisals (both baseline and changes over one week) were responsible for changes in acceptance of living with the disease, although other variables (sociodemographic, clinical, and illness-related beliefs) also played a role. The predictors of change in acceptance of living with the disease differed between analyzed diagnoses. Conclusions: Cognitive factors are an important aspect of the adaptation process to living with an illness. Potential clinical applications and future directions of research are discussed. © 2022 by the authors. Licensee MDPI, Basel, Switzerland.