A trailer-detection system includes a radar-sensor, an angle-detector, and a controller. The radar-sensor is used to detect an other-vehicle present in a blind-zone proximate to the host-vehicle. The angle-detector is used to determine a trailer-angle relative to a host-vehicle of a trailer being towed by the host-vehicle. The controller is in communication with the angle-detector and the radar-sensor. The controller is configured to determine a trailer-presence of the trailer based on the radar-signal and the trailer-angle.