A window trim system and method comprises a trim hoop sized to be slid over an outer face of a window frame to the exterior edge of the frame. A stop member formed around the exterior edge abuts and aligns the trim hoop. A friction member may or may not be installed around the inside of the trim hoop to help hold the trim hoop initially in place. Sealant is then applied around the junction of the trim hoop and window frame on the inside of the trim hoop to fix the trim hoop to the window frame and create a seal against air and water infiltration. The resulting window frame and trim assembly is particularly suited for use in an overfit replacement window installation, but may be used in virtually any window installation.