STUDY OBJECTIVE The Psychomotor Vigilance Task (PVT) is one of the leading assays of sustained vigilant attention in sleep research and highly sensitive to the effects of sleep loss. Even though PVT is widely used in sleep deprivation studies, little is known about PVT performance in patients suffering from sleep-wake disorders. We aimed to quantify the impact of sleep-wake disorders on PVT outcome measures and examine whether PVT can distinguish between healthy controls and patients with sleep-wake disorders and whether PVT can distinguish between three different disorders that express excessive daytime sleepiness. METHODS We compared PVT data of 143 patients and 67 age- and gender-matched healthy controls. Patients were diagnosed with one of the following sleep-wake disorders: narcolepsy with cataplexy (n = 20), insufficient sleep syndrome (ISS, n = 67) and hypersomnia (HS, n = 56). Several PVT outcomes were analyzed: reciprocal mean reaction time, response variability, number of lapses, number of false reaction time, slowest and fastest 10% of reaction time, and duration of lapses. RESULTS PVT performance was generally better in healthy controls than in patients with any of the sleep-wake disorders analyzed. Patients with narcolepsy and HS performed worse on PVT than subjects with ISS. In controls, but not in patients, older subjects had slower reactions times and higher response variability in PVT. CONCLUSIONS PVT performance shows different patterns in patients with different sleep-wake disorders and control subjects and may add useful information to the diagnostic work-up of sleep-wake disorders.