Supernumerary isochromosome resulting in autosomal tetrasomy are rare and have been described only for 12P, 18P, and 9P. Tetrasomy 9P, initially described by Ghymer et al, is a rare chromosomal aberration that has been described in 20 patients. Affected subjects show both cytogenetic and ohenotypic variability. Some patients have the abnormal cell line in all cells, but many display tissue limited mosaicism. The phenotype varies in severity from prenatal death to mild developmental delay and minor anomalies. We reported a infant with mild manifestations of tetrasomy 9p with brief review of related literatures.