"Tiredness", often cited in civil and penal responsibilities secondary to car accidents, hides neurophysiological phenomena which must now be taken into account. The problems of watchfulness in car-driving, is sleepiness, are indeed linked to a genuine disorder in the sleep-wake rythm and attention should be drawn to them in medico-legal cases. Investigations and clinical examinations concerning 110 experts' reports confirm the role played by sleep' disorders in the occurrence of car accidents. Prevention in actually possible. Early detection can take place at various levels and concerns general practitioners, specialists of industrial medicine and specialists for driving tests. In France, the list of diseases associated with, and retraining of a driving license refer only to concentration disorders induced by drug administration, but do not mention sleep pathologies (sleep apnea syndrome, narcolepsy, etc). What is the responsibility of a driver who ignores or says nothing about a sleep pathology from which he is suffering? Is it really necessary to include these pathologies on such a list? It could be more useful to make a large audience; including children, aware of the physiology and pathology of sleep. It appears, from experts' reports, that the management of the problem requires a "driving hygiene".