Abstract: The architectural molding longitudinal groove (50) is a specialty architectural molding trim assembly that includes a longitudinal groove (50) milled along at least one edge in contact with a wall (W). Where applicable, grooves (50) are milled on two or more molding edges. The groove (50) may be provided on window and door casings, baseboard (10) trim boards, chair rail, quarter round, plinth blocks, rosettes, crown molding, and the like. Additionally, the aforementioned architectural molding is not limited to any particular material, but may be created in a number of different types of materials. The longitudinal groove (50) may be applied to wood, plastic, metal, ceramic, natural stone, different composites and manufactured materials. The milled longitudinal groove (50) eliminates the necessity of using masking tape, a painter's straight edge, or extreme care to keep paint off of moldings while painting walls and ceilings.