The occurrence of neonatal lines (NL) in all cusps of the first permanent molar (M 1) has been investigated in complete series of M 1 from 16 males and 11 females. Previous investigations of newborn children gave reason to expect a lower frequency of occurrence in males. The present investigation showed that about one half of the males did not have NL in any of their four M l's, while all females had NL in at least one tooth. This would seem to indicate that on the average boys are less dentally mature at the time of birth than girls. At the same time, it opens up the possibility of a forensic sex assessment. When skeletal remains of children and young persons are in concern.