The aim of this paper is to document the injury rate in high-level modern competitive karate after a change of competition rules was implemented in the year 2000, and to compare it with the injury rate found before the rules were changed. A prospective recording of the injuries resulting from 2,762 matches in three consecutive World Karate Championships (representing 7,425 min of active fighting) was performed, and compared with the results from 2,837 matches from the three last World Karate Championships (representing 7,631 min of active fighting) held before the change of competition rules. In total, 497 injuries were recorded, with an incidence of 0.180 injuries per match or 6.7 per 100 min of active fighting. There were 1,901 male category fights (in which 383 injuries were recorded), and 861 female category fights (in which 114 injuries were recorded). The global injury incidence was almost double with the old rules compared to the one with the new rules [OR 1.99, 95% CI (1.76-2.26); p < 0.00001]. In male category, the risk of injury was higher before the rules were changed [OR 1.81, 95% CI (1.56-2.09); p < 0.00001], and also in female category [OR 2.71; 95% CI (2.64-2.80); p < 0.00001]. The rate of severe injuries was not different before and after the change of rules. The implementation of the new competition rules in competitive karate has been associated with a significant reduction in injury rate, making competition safer for athletes.