Modafinil (Provigil) is approved for treating excessive daytime sleepiness associated with narcolepsy, for shift-work sleep disorder, and as an adjunctive treatment in patients with obstructive sleep apnea syndrome who have residual daytime sleepiness despite optimal treatment with continuous positive airway pressure. Although modafinil improves measures of sleepiness, it does not generally normalize them, and it may be less effective than other stimulants for some narcoleptic patients. We need head-to-head comparisons of modafinil with traditional stimulants in humans to better define its role. We review the current approved and off-label uses of this drug and the evidence behind them.