A patient positioning system for use with a patient on a bed includes a sheet having a bottom surface configured to be placed above the supporting surface of the bed and a top surface opposite the bottom surface, and a wedge having a base wall, a ramp surface, and a back wall, with the ramp surface joined to the base wall to form an apex. The wedge is positioned under the sheet such that the base wall confronts the supporting surface of the bed and the ramp surface confronts the bottom surface of the sheet. The bottom surface of the sheet and the ramp surface of the wedge have engagement members forming a selective gliding assembly that resists movement of the sheet with respect to the wedge in at least one direction and permits movement of the sheet with respect to the wedge in at least one other direction.
