Abstract: An electrical outlet boxholder comprising a generally U-shaped strap member which is adapted to be inserted into an opening formed in a wall member. The strap member comprises a base portion and a pair of legs which depend therefrom. The outer ends of the legs terminate in laterally extending portions adapted to engage the outside surface of the wall member. A retainer is adjustably slidably mounted on each of the legs and has a first portion adapted to engage the inner surface of the wall member. Each of the retainers also has a second portion which is adapted to extend through the opening. The outlet box is inserted into the opening and is received between the retainers. The second portions of the retainers are deformable so that they may be bent inwardly around the outer edges of the outlet box. A modified form of the invention is disclosed for mounting an outlet or light fixture box in an opening formed in a ceiling.