An electrical box extension includes a base, a movable ring and an extension ring. The base has an inwardly extending flange for coupling the base to the open end of an electrical box. The movable ring slides within the base and is captured by a screw that draws the movable ring into the base. The extension ring optionally can be coupled to the top end of the movable ring. A movable support flange can be coupled to the top end of either the movable ring or the extension ring for contacting the outer surface of the wall when the movable ring is drawn into the base.