Abstract: A unitary window insert and method of insertion into a wall structure for forming a finished surround for a window unit. The unitary insert comprises a frame portion sized and shaped to accept a window unit, from which planer finishing wall portions extend to a casing flange which surrounds the interior edge of the insert. Preferably the finishing walls are flared inward creating a pyramidal frustum having an opening larger at the interior surface of the wall than at the exterior surface. The insert extends through the wall structure from an exterior surface and to an interior surface. In the case of poured concrete walls, the insert is provided with a spacer or panel to support the frame portion during construction.