An ultrasonic flow sensor for use in a fluid medium is described. The ultrasonic flow sensor includes at least two ultrasonic converters which are situated in a flow tube offset relative to one another, longitudinally with respect to a flow of the fluid medium. The ultrasonic flow sensor also includes a reflection surface, the ultrasonic converters being set up to exchange ultrasonic signals via simple reflection on the reflection surface. In addition, a deflection device is provided between the ultrasonic converters which is set up to essentially suppress parasitic ultrasonic signals, which are reflected from the reflection surface and which strike the deflection device, by deflection away from the ultrasonic converters.