An adjustable electrical outlet box assembly for mounting a duplex receptacle or similar electrical device within a wall. The adjustable box assembly includes a metal outlet box and a bracket that can slide with respect to the box. An adjustment screw, accessible from the front of the assembly, can be rotated to move the box with respect to the stud it is secured to and thereby adjust the face of the outlet box so that it is substantially flush with the wall surface. The bracket portion of the adjustable box assembly, which may be simply stamped and formed from sheet metal, provides a front plate for securing to the front of a stud and a side plate having widely spaced ears for securing to the side of a stud. The adjustment screw engages straps that are bent outwards from the side plate to enable the bracket to slide with respect to the outlet box.