A method for ascertaining a state of drowsiness of a driver of a motor vehicle, movements of at least one eyelid of one eye of the driver being detected, and the state of drowsiness of the driver being determined as a function of the detected movements. It is provided that an instantaneous normal degree of eye opening is determined, that closing movements of the eyelid are monitored based on the normal degree of eye opening, and that the state of drowsiness is determined as a function of the detected closing movements.