Mosaic trisomy 9 syndrome is a rare chromosomal abnormality and is well defined with dysmorphologic features such as upslanting and short palpebral fissures: deeply set eyes: micrognathia: and cardiovascular, genital, and brain abnormalities. Holoprosencephaly. a developmental brain abnormality, is a rarely seen in patients with mosaic trisomy 9 syndrome. Here we present a case of a patient with mosaic trisomy 9 syndrome with alobar type holoprosencephaly who died in the first hour of the natal period. As per the literature, this is the third case of mosaic trisomy 9 with holoprosencephaly to be reported. Therefore. we believe that holoprosencephaly might take part among the classic dysmorphic features of mosaic trisomy 9 syndrome.