Rheumatoid arthritis (RA) and ankylosing spondylitis (AS) are chronic progressive inflammatory diseases, leading to joint damage and reducing the physical fitness of patients. They are among the most common rheumatic diseases. However, their etiology and symptomatology are different. Formerly, AS was often wrongly diagnosed as RA. Today there are no major diagnostic difficulties in differentiation between these diseases, thanks to modern laboratory tests and imaging. However, a problem may arise when the patient has symptoms typical for both diseases simultaneously. Cases of coexistence of RA with AS – according to our best knowledge – are rare. This study aims to compare our experience in diagnosis and treatment of concomitant RA and AS with the experience of other researchers. Implementation of the proper diagnostic algorithm, allowing for correct diagnosis of both diseases in one patient, may be useful for differential diagnosis of similar cases in the future.