We aimed to determine the distribution of the ABO and Rh blood groups in 832 patients with a tendon rupture. Among these, the frequency of blood group O (52.8%) was significantly higher than in the general population of Hungary (31.1%) and the frequency of group A was significantly lower. Of the 83 cases of multiple ruptures or re-rupture, 57 patients (68.7%) had group O blood. The dominance of group O was found for all sites of tendon rupture, but there was no significant association with the Rh groups. Individuals with blood group O appear to have an increased risk of tendon rupture.