Melatonin is a hormone with indolaminic structure, produced in the pineal gland during darkness, with chronobiological activity that has been known for decades. It is a physiological inducer of sleep and for this indication has been developed as a drug since many years in many international pharmaceutical markets. It has also a relevant antinflammatory and antioxydant capacity that results in beneficial actions on the liver, on cardiovascular diseases, inflammatory processes, in osteoporosis and also in certain tumours. Its neuroprotective action gives founded expectancies of having potential positive effects in several neurodegenerative diseases like parkinson or Alzheimer. It has been recently approved as a drug in the European Medicament Agency (EMEA) and the Spanish Medicament Agency as well. Some of its more relevant pharmacological actions are reviewed.