Trisomy 9 is a rare chromosome abnormality which can occur in a mosaic or nonmosaic state with similar clinical features. The authors present a male with mosaic trisomy 9 from birth to 6 months of life. Clinical manifestations included growth retardation, facial dysmorphism with marked hemi facial hypoplasia and facial asymmetry, single palmar flexion crease, retro calcaneovalgus feet, atrial septal defect, undescended testes and hypospadia. He had several episodes of seizures and ultrasound examination described severe ventriculomegaly, with poorly differentiated parenchyme. These findings are compared to the other previously described cases of trisomy 9 mosaicism through a review of literature.