Study objective: To determine whether the objective level of alertness measured by the Maintenance of Wakefulness Test (MWT) is associated with the occurrence of self-reported sleepiness-related traffic near misses and accidents related to sleepiness in patients with sleep disorders.Methods: This case-control study was conducted over a three-year period in four French sleep centers during a 4∗40 min MWT in patients driving more than 5000 Km/year. Relationship between mean sleep latency on the MWT (MWT latency) and age, sex, driving, sleepiness-related near misses and accidents reported during the previous year, and sleep disorder characteristics was analyzed.Results: Of 377 patients suffering from OSAS, idiopathic hypersomnia, narcolepsy, restless leg syndrome or insufficient sleep syndrome, 176 were included. 74 cases reported an accident or near miss related to sleepiness at the wheel in the past year, and 102 reported no accident/near miss (control patients). Thirty-one (37.8 %) cases and 9 (8.8 %) controls reported being sleepy at the wheel more than once a week (p < 0.0001). After adjusted regression analyses, patients with MWT latency between 19 and 33 minutes had a 3.2- (CI 95%[1.5; 6.8], p < 0.0001) fold increase in risk of reporting a near miss/ accident and patients with MWT latency <19 min had a 5.5- (CI 95%[2.2; 13.8], p = 0.003) fold increase in this risk, compared to the referent group (MWT latency>33 min).Conclusions: MWT latency is associated with self-reported, sleepiness-related near misses and accidents related to sleepiness in the past year in patients routinely investigated in sleep clinics. The MWT could be used to assess driving risk together with clinical interviews assessing sleepiness at the wheel.