During the past decade, advances in genetic research have enabled genomewide discovery of chromosomal copy-number changes and single-nucleotide changes in patients with intellectual disability and autism as well as in those with other disorders. These technological advances — which include array comparative genomic hybridization (CGH), single-nucleotide-polymorphism (SNP) genotyping arrays, and massively parallel sequencing — have transformed the approach to the identification of etiologic genes and genomic rearrangements in the research laboratory and are now being applied in the clinical diagnostic arena.