A two-dimensional knee joint model was developed to estimate forces in selected anatomical structures crossing the knee joint. The model was applied to a specific ski- ing movement in alpine skiing similar to a movement which has been reported to result in rupture of the anterior cruciate ligament. Alpine ski racers were filmed dur- ing training and competition at a location where the movement of interest in this study was likely to occur. The inverse dynamics approach was used to obtain resultant forces and moments about the knee joint as a function of time and knee joint angle for two skiers. These knee joint resultants were distributed to various force carrying struc- tures crossing the knee joint. The muscles, ligaments and bones included in this model were the quadriceps femoris and hamstring muscles, the cruciate and collateral liga- ments and the tibia and femur bones, respectively. Lines of action and moment arms of these structures were obtained as a function of knee joint angle from cadaver data. Additional assumptions were used to reduce the number of unknowns to obtain a mathematically determinate system. The joint equipollence equations were solved for muscle, cruciate ligament and bony contact forces. Several simulations were peformed to assess the sensitivity of the internal force calculations to variations in the inputs and to changes in the load sharing assumptions. Results from the solution of the distribu- tion problem indicated that forces were primarily carried by the quadriceps muscle group, posterior cruciate ligament and bony contact region. The skiers analyzed in the present study did not appear to be at risk of injury to the anterior cruciate ligament, since forces in this ligament were low or non-existent. Conditions leading to forces in the anterior cruciate ligament at flexed knee joint positions were low muscle forces and resultant joint forces directed posteriorly. It was speculated that resultant knee joint extensor moments that can no longer be satisfied by quadriceps muscle forces may be associated with loading conditions that could potentially result in injury to the anterior cruciate ligament.