Objective: The ability to measure skin surface slippage relative to the internal wall of a lower extremity prosthesis under various loading conditions is important for evaluation of socket fit and function, and creation of finite element models. Skin surface three dimensional (3D) shape measurements with tracking of fiducial displacements in situ under axial loading of the prosthesis have not previously been reported. Analysis of slippage within the prosthesis has been performed using a new experimental measurement method based on spiral x-ray computed tomography (SXCT) imaging. Design: Small lead markers were placed on the residuum of an adult with a below-knee amputation, and SXCT scans were obtained with the prosthesis in situ under two static axial loading conditions (44.5N and 178N). The 3D scan data were used to assess slippage with three methods: gross displacement of the tibia and distal end of the residuum: relative displacement of markers; and distance measurements between markers. Results: The markers affixed to the below-knee skin surface within the prosthesis were measured. The skin slipped from 2 to 6mm relative to the internal prosthesis wall when an additional load of 133.5N was applied in the axial direction to the distal end of the prosthesis. The tibial remnant moved 10.0mm distally relative to the prosthesis internal wall. Conclusion: This method provides a feasible means for measuring residuum skin slippage relative to the prosthesis and skin deformation relative to tibia within an in situ prosthesis under load.