Since multiple sclerosis (MS) often affects physically active young individuals, it is important to know if exercise can result in increased disease activity. Therefore we used a self-report questionnaire to examine the relationship of different levels of sports activity and relapses in 632 patients with MS. In order to analyse whether subjective recall might have biased the results, we performed, in a subgroup of our sample, an objective assessment of clinical data and physical fitness parameters. We were unable to find any association between sports activity and clinical relapses in either of the two analyses. The group with highest activity even shows the lowermost mean values, standard deviations and range concerning the number of relapses. Our data suggest that physical activity has no significant influence on clinical disease activity.