Most studies of adolescent sleep habits show a pattern of decreasing total sleep time, a tendency to delay the timing of sleep, and an increased level of daytime sleepiness. Laboratory tests have shown that adolescents do not have a decreased need for sleep but probably need more sleep than prepubertally. A number of factors affect the development of adolescent sleep patterns. Puberty itself imposes a burden of increased daytime sleepiness with no change in nocturnal sleep. Parental involvement in setting bedtimes wanes, though they become increasingly involved in waking teenagers in the mornings. Curfews and school schedules also affect adolescent sleep patterns, seen most commonly as imposing earlier rise times as the school day begins earlier during the adolescent years. Part-time employment has a significant impact on the sleep patterns of teenagers: those who work more than 20 h each week sleep less, go to bed later, are more sleepy, and drink more caffeine and alcohol. Development of circadian rhythms may also play a role in the phase delay teenagers commonly experience. The primary conclusion is that many adolescents do not get enough sleep. The consequences of the chronic pattern of insufficient sleep are daytime sleepiness, vulnerability to catastrophic accidents, mood and behavior problems, increased vulnerability to drugs and alcohol, and development of major disorders of the sleep/wake cycle. Educational programs hold the promise of improving teenagers' sleep patterns through informing youngsters, parents, and pediatricians about proper sleep hygiene and the risks of poor sleep habits.