Abstract: A collapsible cap assembly for a pickup truck or the like includes a pair of track members mounted to the side walls of the pickup truck box, and a series of frame members mounted to the track members. A front frame assembly is stationarily mounted to the track members, and a rear frame assembly and a pair of intermediate frame members are movably mounted to the track members for movement between an extended operative position and a collapsed storage position. A handle is pivotably mounted to the rear frame assembly for assisting in movement of the rear frame assembly and the intermediate frame members between their operative and collapsed positions. A window and door assembly is mounted to the rear frame assembly.