The aim of this study was to quantify clearance mechanics during gait. Seventeen children diagnosed with hemiplegic cerebral palsy underwent a three-dimensional gait analysis evaluation. Dynamic leg lengths were measured from the hip joint center to the heel, to the ankle joint center and to the forefoot throughout the gait cycle. Significant asymmetry was observed during stance, initial and terminal swing phases, where the hemiplegic limb was found shorter by using a paired "t"-test at 51 sample points (p < 0.05). The hemiplegic side was restricted in achieving maximal length during terminal swing. The ratio between the maximal dynamic leg length during the stance phase to minimal dynamic leg length during the swing phase was found higher on the non-involved side and lower on the hemiplegic side (p < 0.05). Quantifying clearance mechanics based on dynamic leg length can provide an additional insight into the analysis of gait patterns and might assist in detecting time of abnormal kinematic deviations.