Originality Several reports have described melatonin secretion in older children, but only a few have observed melatonin concentrations during the first year of life. Very little is known about the fetal pineal melatonin synthesis and nothing at what prenatal age melatonin synthesis starts. Premature infants have a 3 months delay in the development of melatonin rhythmicity compared to full-term infants. One study found discordant data with decreasing melatonin value around term. The absence of longitudinal study and the low number of children included make the interpretation difficult of the secretion of melatonin at the newborn.