There is limited data in the literature on the normal size of the anterior fontanelle. This cross- sectional study was to determine normal values of anterior fontanelle size on the first day of life, using standard methods. Anterior fontanelle size was measured in 400 term and healthy neonates delivered at the Shariati Hospital, Tehran, Iran. Examination included assessment of head circumference, anterior fontanelle size, weight, length. Type of delivery was also recorded. The mean size of anterior fontanelle was 25.34 ± 13.27 mm, and it was established in both genders, 26.70 ± 13.19 mm in boys, and 23.67 ± 13.20mm in girls. A significant difference between the mean anterior fontanelle size in boys and girls was found (P=0.023). There was no significant difference in anterior fontanelle size between the infants born with a normal vaginal delivery and those with cesarean-section (P=0.08). There was found a significant negative correlation between the mean size of anterior fontanelle size with both weight and height (P