A considerable number of central nervous system pathologies remain undiagnosed during the first two trimesters of pregnancy. This group of disorders includes anomalies of brain proliferation, migration and cortical organization. Due to the fact that a detailed ultrasound examination of the fetal brain is usually not performed during the third trimester the diagnosis of these disorders is usually only made in families with a previously affected child or in many cases be mere chance. In this article we review the feasibility of prenatal diagnosis of disorders of brain proliferation: microcephaly, macrocephaly, hemimegalencephaly and neoplastic and non-neoplastic abnormal cell types. We discuss the differential diagnosis and offer a stepwise approach to the diagnosis of the more common disorders.