A case of alobar holoprosencephaly diagnosed at 10 + 3 weeks' gestation by transabdominal and transvaginal ultrasound examination followed by histological confirmation is presented. The diagnosis was based on two sonographic criteria: intracranial finding of a single ventricle with a mantle and no visible midline structures but fusion of the thalami and corpus striatum, and facial abnormalities, including hypotelorism and proboscis. The fetal karyotype was triploidy. The ultrasound findings were confirmed by pathological examination. The histological findings of proboscis, single lens and single ventricle with neural tissue remnants are presented.