With the ultimate goal to better demonstrate the biomechanics of spastic paretic stiff-legged gait, we simulated the motion of this gait disability, based on actual kinematic gait data. We created and applied a seven link-segment forward dynamic model to the gait kinematics of five adult subjects with this gait disability as a result of stroke. Trunk and limb segment torques developed during the affected limb's swing period of gait were calculated via inverse dynamic techniques from the measured kinematic data and incorporated into the forward dynamic model to simulate motion. In each case, the simulated motion corresponded to the directly measured kinematics. The hip and knee torques were then altered to predict potential resultant changes in knee flexion. Preliminary results suggest a stronger effect of hip torque than knee torque on knee angle, which also qualitatively corresponded with clinical data. This study demonstrates the feasibility of forward dynamic modelling based on actual clinical data and provides a further means to analyze potential mechanisms of this gait disability. Copyright 1997 Elsevier Science B.V.