The authors examined whether there were gender differences in the variability of basic gait parameters (stride length, stride time) and 3-dimensional (3D) rotations of the hip, knee, and ankle joints during treadmill locomotion of 18 men and 15 women at 4 different gait speeds (walking at 5 km/hr, running at 8, 10, and 12 km/hr). The authors used 2-way analyses of variance to assess the data. No gender differences in the mean values or variability of basic gait parameters were detected. However, the women exhibited lower variability than did the men for 6 individual joint rotations: (a) transverse plane rotations of the ankle joint at 8, 10, and 12 km/hr, (b) transverse plane rotations of the hip and knee joints at 12 km/hr, and (c) sagittal plane rotations of the ankle joint at 12 km/hr. When collapsed across all 3D lower extremity rotations, the data showed that the women had lower variability than did the men at 12 km/hr. Reduced variability may result in more localized mechanical stress on anatomical structures and could therefore be a risk factor for injury in women at high gait speeds. The results also suggested that gender differences in variability may not be consistent across different levels of the motor system.