An ultrasonic sensor is described having a housing which has a circumferential side wall and a base surface. A transducer element for generating ultrasonic vibrations is mounted on the base surface. The side wall includes a lower side wall section, in which the side wall has an essentially rotationally asymmetrical profile in a plane parallel to the base surface, and an upper side wall section in which the side wall changes to an essentially rotationally symmetrical profile toward an upper edge of the side wall. In other respects, the present system provides a parking assistance system for a vehicle, having a control unit and such an ultrasonic sensor, as well as a method for manufacturing an ultrasonic sensor.