Non-24-hour sleep-wake rhythm disorder is a circadian rhythm sleep-wake disorder characterized by an inability to entrain to the 24-hour environment. Patients present with complaints of insomnia or hypersomnia, with progressive daily shifts of sleep-wake activity on actigraphy or sleep logs. Although first recognized in blind individuals without light perception, it also can be seen in individuals with intact vision. Treatment focuses on timed melatonin in blind individuals, whereas it is more complex in sighted individuals, using multiple time cues, such as light, melatonin, social interactions, feeding, and activity.