A set of exercises--the "11"--have been selected to prevent football injuries. The purpose of this cluster-randomized controlled trial was to investigate the effect of the "11" on injury risk in female youth football. Teams were randomized to an intervention (n=59 teams, 1091 players) or a control group (n=54 teams, 1001 players). The intervention group was taught the "11," exercises for core stability, lower extremity strength, neuromuscular control and agility, to be used as a 15-min warm-up program for football training over an 8-month season. A total of 396 players (20%) sustained 483 injuries. No difference was observed in the overall injury rate between the intervention (3.6 injuries/1000 h, confidence interval (CI) 3.2-4.1) and control group (3.7, CI 3.2-4.1; RR=1.0, CI 0.8-1.2; P=0.94) nor in the incidence for any type of injury. During the first 4 months of the season, the training program was used during 60% of the football training sessions, but only 14 out of 58 intervention teams completed more than 20 prevention training sessions. In conclusion, we observed no effect of the injury prevention program on the injury rate, most likely because the compliance with the program was low.