BACKGROUND: Holoprosencephaly is a structural anomaly of the brain that consists 
in a defect of the prosencephalon development that leads to face and 
neurological defects of variable intensity.
AIM: To estimate holoprosencephaly prevalence at birth.
PATIENTS AND METHODS: All cases of holoprosencephaly, born alive or stillbirths, 
registered in the 15 Chilean Hospitals of the Latin American Collaborative Study 
of Congenital Malformations (ECLAMC) between 1972 and 2012, were studied. 
Craniofacial and other anomalies found in newborns affected by holoprosencephaly 
are described.
RESULTS: Fifty five cases of holoprosencephaly (58% males) were found among the 
798.222 registered births (rendering a prevalence at birth of 0.69 per 10.000 
newborns). The most common cranial defect was medial cleft lip with cleft palate 
(27.3%), bilateral cleft lip (11%) or both (38.2%), cyclopia (14%), single 
nostril (10.9%) and proboscis (9.1%). Eleven percent cases had a trisomy 13. A 
slight increase in prevalence over time was observed.
CONCLUSIONS: Holoprosencephaly has a low frequency in Chile and is associated to 
trisomy 13. The increase in prevalence could be explained by a better prenatal 
diagnosis (ultrasonography).