Sleep problems are common and often increase when initiating pharmacotherapy for ADHD. Stimulants are commonly associated with delayed sleep onset/insomnia although nonstimulants can be associated with daytime sleepiness. There is a wide variability in severity and duration of sleep effects, but most effects are mild and improve over time. Although sleep problems occur in all age groups, preschoolers and adolescents appear to be more vulnerable to adverse effects on sleep than adults and children. Interventions to improve sleep include behavioral therapy, changing dose schedules or formulations, and adding a sleep-promoting agent such as melatonin.