Sleep and sleep medicine are in the limelight of the researchers for thousands of years. The definition of sleep started to change in the light of scientific experiments performed in the twentieth century, and the number of investigations on sleep medicine increased tremendously. Effects of nutritional factors on the regulation of the sleep-wake cycle and central nervous system triggered new developments in sleep medicine. Tryptophan is an essential amino acid and a precursor of serotonin, melatonin, and nicotinamide. More recently, the role of tryptophan played in the sleep-wake rhythm of newborns has been an interest of research. High levels of tryptophan are associated with the improvement in the total hours and the efficiency of sleep and increase in the duration of nocturnal immobility and decrease in both the number of nocturnal awakenings and the sleep latency of newborns. Serotonin is named as "neurohormone of sleep" after understanding the key role of serotonin in the mechanisms of the sleep-wake cycle. Inhibition of tryptophan hydroxylase enzyme decreases both the synthesis of serotonin from tryptophan and serotonin levels significantly leading to insomnia. The serotonergic system has a crucial impact on sleep and airway stabilization. Majority of investigations on serotonin have shown that serotonergic system is related to obstructive sleep apnea syndrome (OSAS). Melatonin is secreted by the pineal gland. It is synthesized from 5-HT by pinealocytes and then released into the blood and cerebrospinal fluid. It is well known that melatonin affects sleep, circadian rhythm, puberty, antioxidant status, aging, and blood pressure. Contrary to other sleep disorders, scarce data on the involvement of melatonin in OSAS are available. Investigators have shown that plasma melatonin levels are low in patients with newly diagnosed OSAS. Elaborate prospective studies should be conducted while bearing in mind the drawbacks of aforementioned studies to better delineate the role of tryptophan and its products in the pathogenesis, adverse outcome of sleep disorders and to answer whether consumption of tryptophan-rich foods and its products might be a novel pharmacological treatment or not in sleep medicine.