The meeting started with a thorough training session discussing many examples of joints and features showing repair.These features were filling-in of erosions, recortication, sclerosis,remodelling, reconstitution of a normal joint, and trabeculation. The definitions were refined as compared with the previous exercise, and trabeculation was added as a feature that can help in distinguishing progression from repair. Filling-in, although clearly a reduction in the size of erosions, was thought by some to have additional information. Because recortication implies that the reader has concluded that the case is one of healing, in conducting the exercise readers recorded cortication of erosions and noted whether this was better or worse in the paired individual joints without regard to whether the reader had an opinion as to whether the pair showed progression or repair. It was also recognized that reconstitution of normal structure required a prior judgement as to whether repair was present.Two exercises were performed thereafter on two consecutive days. The third exercise was performed separately by two readers not involved in the first two exercises. Images for all three exercises were selected by one of the experts (JTS), who did not participate in the assessments, from a large set of radiographs available in digitized form from several data sources. Sixty-four image sets were selected,knowing the time sequence; approximately equal numbers of cases with repair, progression and equivocal or no change were included