A selectively powered ambulatory stretcher chair has a bifurcated articulating base of free-wheeling casters at each of the corners thereof, with motor driven wheels on a transaxle interposed therebetween. Articulation of the bifurcated base causes deployment and retraction of the drive wheels to allow use of the stretcher chair in both a manual and power-driven mode, while ensuring stability in both. A u-shaped positionable bar is pivotally connected to a back of the stretcher chair and maintains a control box within a tight range of positions as the chair of the stretcher chair assembly translates between upright and horizontal positions. The back of the stretcher chair is of a radiolucent material, accommodating medical procedures in the stretcher chair in a broad range of positions.