Melatonin is a, widely distributed and important signal molecule that occurs in unicellular organisms, plants, and fungi in addition to animals and humans. It is the main hormone of the pineal gland and its synthesis occurs mainly in this gland. It has free radical scavenging and antioxidative properties and shows clinical antibacterial and analgesic effects. By means of these properties, it is able to protect cells, tissues, and organs against oxidative damage from free radicals. Recently, widespread interest has grown among researchers regarding the apparent protective effects of melatonin following traumatic events to peripheral nerves, especially the sciatic nerve and its pathological conditions, as melatonin administration could be beneficial following surgery. Although there are great numbers of studies that have mentioned protective effects of melatonin on peripheral nerve pathologies, there are also some studies that report toxic effects of melatonin on peripheral nerves. This paper reviews the available literature in terms of both the beneficial and the toxic effects of melatonin on peripheral nerves. Short descriptions of the structure of pineal gland and synthesis and secretion of melatonin are also given.