The aim of this study is to describe the prevalence and incidence of lower extremity injuries occurring before and during the Rotterdam marathon, and to evaluate the impact of the injuries. A cohort study was compiled of recreational male participants in the 2005 Rotterdam marathon. Demographic data and information on previous injuries were obtained from participants using a baseline questionnaire. Information on injuries sustained shortly before or during the marathon was obtained from a post-race questionnaire. Seven hundred and twenty-five (48.3%) participants returned the baseline questionnaire. The 1-year prevalence of running injuries was 54.8%. In the post-race questionnaire, 15.6% of all respondents reported at least one new lower extremity injury in the month preceding the Rotterdam marathon. The incidence of lower extremity injuries occurring during the marathon was 18.2%; most of these injuries occurred in the calf, knee and thigh. Immediately after the marathon the median score of pain intensity at rest was 2 points vs 4.5 points during physical exercise. Hence we can conclude that running injuries are very common among recreational male marathon runners. However, the pain severity and consequences for work and daily activities seem to be relatively low 1 week after the marathon.