A warning system for a motor vehicle includes sensor devices for detecting a driving situation, a warning device for the output of a warning to a driver of the motor vehicle, a device for detecting the driver's state of attention that includes operating elements of existing vehicle components, and a control device which triggers the warning device as a function of data of the sensor devices and the device for detecting the state of attention. In this warning system, the device for detecting the state of attention infers a reduced degree of driver attention when a total duration of a sequence of several operating actions related to the operating elements exceeds a minimum duration. A conclusion can also be drawn that the degree of driver attention is reduced when operating inputs are triggered that are known a priori as being cognitively demanding, for example, operating a telephone keypad.