Circadian rhythms are changed in patients with rheumatoid arthritis. A new modified-release delivery system has been developed which adapts the release of the administered glucocorticoid to the circadian rhythms of endogenous cortisol and disease symptoms to improve the benefit-risk ratio of glucocorticoid therapy in rheumatoid arthritis. We aimed to assess the efficacy and safety of a new modified-release prednisone tablet compared with immediate-release prednisone in patients with this disease.