Recent advances in genetics and neuroimaging have greatly contributed to our understanding of the spectrum of midline brain and craniofacial malformations known as holoprosencephaly. This review summarizes our current understanding of the epidemiology and molecular-genetic bases of these malformations, as well as recent neuroradiological and clinical studies, which have revealed that the manifestations of holoprosencephaly are far more variable than previously appreciated. We also discuss the implications for and importance of accurate diagnosis, prognosis, management of common medical problems, and counseling for affected families.