Abstract: A jig for assembling a rebar pier cage wherein certain of the individual jig elements are laterally and longitudinally adjustable to provide a jig capable of assembling rebar pier cages of various sizes and shapes. The jig elements comprise a plurality of rebar stirrup retaining elements removably secured within longitudinal openings in first and second, elongated channel bars which traverse a rectangular work surface in parallel relationship. Opposite ends of the first and second channel bars are slidingly secured within longitudinal openings of third and fourth channel bars which laterally span the opposite, shorter edges of the work surface. Means are provided to adjust the longitudinal spacing between each stirrup retaining element in the first and second channel bars, and also the lateral spacing between the first and second channel bars.