A tool for positioning molding, such as crown molding, during installation, has a base member adapted to be releasably hung on a wall near the ceiling. A retaining member is vertically slidably mounted on the base member and has an upper end portion disposed at an acute angle to hold a piece of molding at a desired attitude between the retaining member and the wall. The retaining member is slid and locked In vertically and locked in position to hold the molding in place while it is fastened to the wall, after which the tool is removed from the wall.