A work classification of ankylosing spondylitis is presented including such novel concepts as the stage of the disease (instead of sacroiliitis), extra-axial and extra-skeletal manifestations. Modern approaches to the evaluation of disease activity are described Extensive explanations of these notions are presented together with the recommendations on formulation of diagnosis. The advent of new and more eficacious methods of visualization as well as more sensitive and specific criteria for inflammatory nature of back pain are considered The authors modified the traditional criteria for ankylosing spondylitis and developed their version to be verified in clinical practice in this country.