A jamb and frame combination for doors and windows having an elongated L-shaped cross section member adapted to fit snugly against two abutting side portions of a window or door casing, and including a tongue portion along one distal side portion and extending the length thereof, and at least one removable fastener adapted to pass through the L-shaped cross section member in an area adjacent to the tongue portion and into the window or door casing to thereby hold the L-shaped cross section member snugly thereto. An elongated trim member including a groove portion extending the length thereof and adapted to interlock with the tongue portion of the L-shaped cross section member, such that when the L-shaped cross section member is installed upon a window or door casing, the trim member groove portion can be pushed upon the L-shaped cross section member tongue portion and frictionally held in place and covering the at least one removable fastener.