Abstract: An adjustable bed frame assembly includes a clamp which fits with two aligned and overlapping frame rails, including horizontal and vertical legs of the frame rails, to enable relative adjustment of the frame rails and to fix the bed frame at a set dimension. A leg mount extends from the clamp with a structure for mounting a vertical leg for additional elevation and support of the bed frame. The vertical extent of the leg is also adjustable by interconnection with one or more extension pieces. The configuration of the clamp and the leg mount both stiffens the bed frame and provides a very rigid support member for the bed frame. The leg mount can be formed from a single piece of metal with an open seam, and the extension pieces can be formed from a single piece of metal with an open seam.