About 1 of 10 night-shift workers suffers from severe excessive sleepiness on the job. This realization has led to the development of specific diagnostic criteria for people affected with shift-work sleep disorder. In this multicenter study, patients meeting this case definition were treated with placebo or modafinil. Although there was a significant improvement in laboratory measures of sleep, treated patients were still quite sleepy. Modafinil improves performance among patients with shift-work sleep disorder but does not come close to returning them to a normal level of sleepiness. Nearly 6 million Americans work at night on a permanent or rotating basis. 1 Night-shift work disrupts both sleep and waking because of the misalignment of circadian regulation and sleep–wake behavior. 2 , 3 In about 5 to 10 percent of night-shift workers, the sleep–wake disturbance is severe enough to warrant diagnosis as shift-work sleep disorder, 4 – 6 which is characterized by a level of excessive sleepiness during night work and insomnia when attempting to sleep in the daytime that is judged to be clinically significant. 4 , 5 Persons with shift-work sleep disorder miss family and social activities more frequently and have higher rates of . . .