Purpose: Sex and history of anterior cruciate ligament (ACL) injury are risk factors for developing knee osteoarthritis (OA). Women demonstrate a 45% increased risk of developing knee OA compared to men and individuals with a history of ACL injury are four times more likely to develop post-traumatic knee OA compared to individuals without a history of knee injury. Women are also more likely to sustain secondary ACL injuries and may be at greater risk of subsequent knee articular cartilage damage because ACL re-tears are associated with worse concomitant chondral damage. Jump landing differences exist between men and women before ACL injury that may predispose women to an increased risk of primary ACL injury. However, it is unclear if men and women with a history of ACLR have different movement patterns during jump landing tasks that may predispose women to secondary ACL injury. Therefore, purpose of this cross-sectional laboratory study was to assess single leg landing lower extremity kinematic and kinetic differences between men and women with a history of ACLR. Methods: A total of seventeen men (age = 23.3±4.0 years, BMI = 23.3±2.7 kg/m2, time since surgery = 40.0±27.2 mo.) and thirty-five women (age = 22.7±4.7, BMI = 25.3±3.8 kg/m2, time since surgery = 36.7±22.3 mo.) completed three trials of a single leg drop crossover hop (SLC) on their ACLR limb. Tri-planar lower extremity kinematics and kinetics in addition to vertical ground reaction force (vGRF) during the task were assessed via a 10-camera motion capture system and single embedded force plate sampled at 240 and 1200 Hz respectively. Participants were asked to jump from a 30 centimeters (cm) tall box onto the center of the force plate 40 cm away. After landing onto the force plate, participants continuously hopped diagonally as far as possible along a 45⁰ angle. Ground contact time (GCT) with the force plate before the cross-over portion of hop was defined from initial contact (vGRF>10 N) to take-off (vGRF<10 N). Ensemble averages and associated 90% confidence intervals of tri-planar knee and hip kinematics and kinetics were calculated across 100 data points of GCT for men and women. GCT of the SLC was separated into an eccentric deceleration phase (0-50%) and concentric preparatory phase (51-100%). Significant between group sex differences were determine if the lower extremity kinematic and kinetic ensemble average confidence intervals did not cross for three consecutive data points of ground contact time. Peak average biomechanical outcomes between men and women were extracted during significantly different time points. Results: Women demonstrated smaller knee flexion angles for more than two-thirds of GCT compared to men (sagittal plane knee angle: men = 59.8±10.6⁰, women = 49.7±13.6⁰). Women also demonstrated greater frontal knee plane kinematic motion at initial contact (frontal plane knee angle: men = 3.5±4.2⁰, women =-0.5±6.2⁰) and near take off (frontal plane knee angle: men = 1.9±6.9⁰, women =-1.9±4.5⁰) compared to men. Men landed with greater tri-planar hip and knee moments throughout GCT especially during the middle of the concentric phase compared to women. Men demonstrated greater hip extension (men=-2.2±1.1 Nm/kg, women=-1.1±0.7 Nm/kg), adduction (men=-1.3±0.4 Nm/kg, women=-0.9±0.5 Nm/kg) and internal rotation (men=-0.8±0.4 Nm/kg, women=-0.5±0.3 Nm/kg) moment than women. Men also demonstrated greater knee extension (men=-1.3±0.5 Nm/kg, women=-1.0±0.5 Nm/kg), abduction (men=-0.7±0.5 Nm/kg, women=-0.3±0.5 Nm/kg) and external rotation (men=0.5±0.3 Nm/kg, women= 0.3±0.2 Nm/kg) moment than women. Conclusions: The SLC task is complex because it involves unilateral limb control and preparation for lateral movement that may place the knee in a position of greater risk for ACL injury. Greater frontal plane and lesser sagittal plane knee kinematics during landing indicate poor load dissipation and are associated with increased risk of primary and secondary ACL injury. Women demonstrated greater knee abduction angles and lesser knee flexion angles compared to men which may place them at increased risk of sustaining a secondary ACL injury. Additionally, men landed with greater knee and hip tri-planar moments during the middle concentric phase of GCT and hopped significantly farther than women. These results suggest that women may inefficiently store and transfer energy during jump preparation to protect the knee which negatively impacts functional performance. Implementing movement retraining strategies and eccentric strength interventions helps improve stiff landing mechanics and improve the transition from eccentric loading to concentric preparation for better hop performance. High-risk landing patterns should be addressed through secondary injury prevention efforts in women to reduce secondary ACL injury and increased knee articular cartilage damage.