Comparative genomic hybridization (CGH) has been developed as a molecular test for chromosomal analysis and it is used in prenatal diagnosis, pediatric patients, or adults with specific indications. CGH detects microdeletions and microduplications that are more than 500 base pairs and they are not detected by karyotype. In 2010 a consensus document and an economic analysis were published suggesting that CGH should be considered as the first diagnostic test, replacing karyotyping in patients with neurological problems, autism, and cognitive deficits and in newborns with congenital anomalies of unknown etiology. CGH is based on the simultaneous hybridization of differentially labeled test and normal reference DNAs to normal metaphase chromosomes. The hybridized DNAs are detected with two different fluorescent dyes.