Abstract: A cover (10) for an air conditioner (29) mounted in the wall (11) of a building. The cover (10) has a back panel (13), four side wall panels (14, 15, 16, 17) which extend from the back panel, a flange (20) which extends around the periphery and is formed integrally with the side walls, and a sealing strip (30) of compressible weatherstripping material which is adhered to the inner surface of the flange in position to seal against the wall around the periphery of the air conditioner. Retainers (22) are secured to the wall adjacent the flange (20) and are adapted to engage the flange and thereby press the sealing strips (30) tightly against the wall. A modified cover (40) has a short top side wall (43) with a clip connection strip (53) having weatherstripping (54) thereon to seal up against the face of the window frame where the air conditioner is mounted immediately beneath a window.