Background Head growth and anterior fontanel (AP) closure are passive processes in response to brain growth. The growth of the brain and skull starts in the third week of intrauterine gestation. roth processes run simultaneously as a part of integral growth, along 'With increasing gestational age, until post?birth. Measurement of head circumference (He) and AF in newborns is done to determine if the brain and skull grew normally during the intrauterine period. Objectives To investigate the differences in He and AF size between preterm and full?term infants, and the relationship between gestational age (GA) and birth weight (BW) to He and AF size. Methods This was a descriptive analytic study on preterm and full?term newborns. Measurement of HC and AF was conducted in three phases: just after birth, 1x24 and 2x24 hours of age. Analysis of HC and AF size differences between preterm and full term subjects was performed, as well as analysis of the correlation between GA and BW to HC and AF size. Results Two hundred fifty newborns completed the study. There were 180 full?term and 70 preterm subjects. Median HC in full? term and preterm male subjects were 34 cm (range 31?37 cm) and 31 cm (27?34 cm), respectively. Median HC in full?term and preterm female subjects were 33 cm (31?36 cm) and 32 cm (27?3S.S cm), respectively. Median AF in full?term and preterm male subjects were 2.17 cm (1.0SA.6 cm) and 2.22 cm (1.3SA.S cm), respectively, and in full?term and preterm female subjects were 2.02 cm (lA.1S cm) and 2.22 cm (0.7SA cm), respectively. The HC of preterms were significantly lower than the fullterms (P<O.OOl), however the AF size was not different between these 2 groups of newborns (P =0 .28). Correlation test between GA and BW to HC size revealed a positive correlation (r=0.620, P<O.OO 1 and r=0.801, P<O.OOl, respectively), but not to AF size (r=? 0.06, p@ 0.279 and F- 0.049, P@0.44, respectively). Conclusions We found that the HC size of pre terms was significantly lower than the full terms, but no significant differences in AF size between the two groups. GA and BW were associated with HC size, but not associated to AF size.