Abstract: An adjustable cornice that can expand in width to accommodate window fixtures of various dimensions without necessitating cutting. The adjustable cornice is assembled from a central section that attaches to a set left and right runners. The runners serve as the mounting system for the additional sections that include the plurality of left and right extension sections, and the left and right end sections. The runners traverse through the extension sections. The adjustable cornice conforms to a desired width by adding or removing the extension sections. The runners then traverse into the end sections and a plurality of fasteners are used to affix the runners to the extension sections, the end sections, and the central section. Once the front facing sections are affixed, the side sections are attached to the end sections and brackets are affixed to provide a method of mounting on the walls surrounding a window fixture.