Sleep is a physiological condition characterized by a reversible behavioral state with changes in the level of awareness and responsiveness to stimuli and plays a fundamental role related to electrophysiological, neurochemical, anatomical and functional changes of the brain. It is controlled by chronobiological and homeostatic mechanisms and is intensely related to the periods of wakefulness. One of the most immediate results of the poor quality of sleep is the drop in performance on the next day, causing damage during wakefulness, such as drowsiness, mood fluctuations, anxiety, low self-esteem, slow thinking, memory loss, poor school and personal performance, and predisposition to accidents. Sleep plays an important role in the physical and emotional development of adolescents, who are going through a period of intense learning and differentiation. Paradoxically, however, nowadays, several factors contribute to the poor sleep of adolescents because of the social pressures that boost their activities such as excessive use of computer and phone, new affective relationships, parties, etc. All of these factors determine a reduction of nighttime sleep and consequent daytime sleepiness. The objective of the present study was to present some issues related to the physiology of the sleep-wake cycle and its implications in the daily life of teenagers, in an attempt to stimulate the thinking of professionals about the important aspects related to quality and quantity of sleep.