Reports of reduced daytime sleepiness following extended nighttime sleep in normal, regular sleepers suggest that they (and perhaps much of the general population) are chronically sleep deprived. However, 1) the social and environmental contexts of sleep allow for much intraindividual variation in sleep duration and structure; 2) animal studies show that when there is opportunity for sleep and few incentives to remain awake, sleep occurs for reasons other than in response to a physiological requirement, i.e. sleep satiation may precede actual awakening, 3) accounts of increased sleep duration earlier this century are flawed and 4) because increased sleep onset latency and wake after sleep onset are features of extended sleep, it would be difficult to persuade people to sleep longer for the small benefits to daytime alertness. Laboratory studies show that 1) following extended sleep the improvements in daytime alertness are minor, even by the Multiple Sleep Latency Test (MSLT), and could be achieved equally successfully and with less disruption to habitual daily patterns by taking a short nap; 2) normal subjects extend sleep at night not necessarily because they are chronically sleepy, because there may be no prior MSLT signs of daytime sleepiness; 3) mood effects of extended sleep are confounded by earlier bedtimes; and 4) extended sleep does not necessarily make subjects feel well rested immediately on waking. In sum, most people are not chronically sleep deprived but have the capacity to take more sleep, in the same way that we eat and drink in excess of physiological needs.