We examined two methods of calculating radiological progression in rheumatoid arthritis using hand and wrist radiographs scored by Larsen's method. Progression over 12 months was calculated in two ways: absolute change in score; relative change in score. The two methods of scoring progression were investigated in two studies. In the first 173 patients with rheumatoid arthritis treated with a variety of non-steroidal and slow-acting anti-rheumatic drugs were evaluated. There were different results using absolute and relative changes in score. Relative changes gave more meaningful results. The second study looked at 80 rheumatoid patients treated with slow-acting drugs for 6 months; patients with a persistently high ESR had significantly more progression assessed by relative change but not by absolute change. Evaluating the progression of joint damage by methods employing a scoring system must be interpreted with caution. Relative change may provide a more valuable measure than absolute change.