This study analyses the motion of the residual femur within a trans-femoral socket during gait using ultrasound data from two simultaneously transmitting transducers connected to two ultrasound scanners. Calibration tests accurately established the orientation of the two transducers mounted on the lateral wall of the socket. Relative positions of the ultrasound image of the femur were measured on video playback. Motion of the residual femur, relative to the lateral wall of the socket, at any instant during gait may be estimated, if the relative positions of the two transducers and the motion of the ultrasound image are known. A consistent pattern of femoral motion during 10 gait cycles is displayed graphically. The femoral motion in this paper is expressed as abduction/adduction or flexion/extension relative to the socket. However, without a full gait analysis study, the orientation of the socket relative to the ground or relative to the pelvis cannot be determined.