The contrast between clinical improvement and radiological deterioration in rheumatoid arthritis (RA) is striking. We characterized this relationship using serial disease activity measures and radiographs of hands and feet in 40 RA patients observed over 6 yr. All disease activity measures improved, including grip strength, Ritchie index (RI), haemoglobin and erythrocyte sedimentation rate (ESR) (all P < 0.0001). In contrast, articular erosion increased (P < 0.0001). Radiological change during the study correlated with RI (r = 0.49), haemoglobin (r = -0.56) and ESR (r = 0.53). Radiological status at review also correlated with these variables (r = 0.36, -0.44 and 0.36, respectively). Articular erosion continues in RA despite clinical improvement and is accelerated in those with evidence of continuing synovial inflammation, reflected in clinical and laboratory measures of disease activity. Since many therapies in RA suppress inflammation, but not erosion, these findings suggest that the pathogenesis of articular erosion may differ from that of synovial inflammation.