['Few prospective studies have investigated the biomechanical risk factors of anterior cruciate ligament (ACL) injury.', 'To investigate the relationship between biomechanical characteristics of vertical drop jump (VDJ) performance and the risk of ACL injury in young female basketball and floorball players.', 'Cohort study; Level of evidence, 3.', 'At baseline, a total of 171 female basketball and floorball players (age range, 12-21 years) participated in a VDJ test using 3-dimensional motion analysis. The following biomechanical variables were analyzed: (1) knee valgus angle at initial contact (IC), (2) peak knee abduction moment, (3) knee flexion angle at IC, (4) peak knee flexion angle, (5) peak vertical ground-reaction force (vGRF), and (6) medial knee displacement. All new ACL injuries, as well as match and training exposure, were then recorded for 1 to 3 years. Cox regression models were used to calculate hazard ratios (HRs) and 95% CIs.', 'Fifteen new ACL injuries occurred during the study period (0.2 injuries/1000 player-hours). Of the 6 factors considered, lower peak knee flexion angle (HR for each 10° increase in knee flexion angle, 0.55; 95% CI, 0.34-0.88) and higher peak vGRF (HR for each 100-N increase in vGRF, 1.26; 95% CI, 1.09-1.45) were the only factors associated with increased risk of ACL injury. A receiver operating characteristic (ROC) curve analysis showed an area under the curve of 0.6 for peak knee flexion and 0.7 for vGRF, indicating a failed-to-fair combined sensitivity and specificity of the test.'] Do stiff Landings Are Associated With Increased ACL Injury Risk in Young Female Basketball and Floorball Players?