This invention pertains to an adjustable cover for an electrical outlet box. The cover is configured having a generally planar mounting plate with a collar surrounding an opening through this mounting plate. An extension sleeve moves within this opening and adjacent the collar. At least one fastener is located adjacent the opening and is movable between a locked position and an unlocked position. The fastener operates a locking device that engages a wedge against the extension sleeve when the fastener is in the locked position and disengages a wedge against the extension sleeve when the fastener is in the unlocked position.