The primary symptom of microcephaly is having a head size that is much smaller than that of other children of the same age and sex. Head size is a measure of the distance around the top of the child's head (circumference). Using standardized growth charts, health care providers compare the measurement with other children's measurements in percentiles. Some children just have small heads, with a measurement that falls below an established value for children of the same age and sex. In children with microcephaly, head size measures much smaller than average for the child's age and sex. A child with more-severe microcephaly may also have a sloping forehead.