Virtually all forms of microcephaly display some degree of simplification of the cortical gyral pattern, with fewer gyri and shallow sulci. Two particular modes of neural progenitor division in the developing cerebral cortex are symmetric and asymmetric. In asymmetric divisions, radial glial progenitors in the ventricular zone (VZ) give rise to a post-mitotic neuron and a radial glial daughter that re-enters the cell cycle. Disruption of neural progenitor proliferation is but one path leading to microcephaly. Seizures are a manifestation of microcephaly that occurs with variable frequency, according to the clinical syndrome and causative gene. The first-line diagnostic test for microcephaly is an accurate measurement of occipital-frontal circumference (OFC) obtained in the delivery room and repeated at each postnatal office visit. The ability to distinguish between congenital microcephaly and postnatal microcephaly will be helpful in prioritizing the possible etiologies.