A microdeletion at chromosome 22q11 is the most frequently known interstitial deletion found in humans, occurring in approximately one of every 4000 live births. Its occurrence is associated with a characteristic facial dysmorphology, a range of congenital abnormalities, and psychiatric problems, especially schizophrenia. The prevalence of psychosis in those with 22q11 deletion syndrome is high (30%), suggesting that haploinsufficiency of a gene or genes in this region may confer a substantially increased risk. In addition, several studies provide evidence for linkage to schizophrenia on 22q, suggesting that a gene in this region could confer susceptibility to schizophrenia in nondeleted cases. Recent studies have provided compelling evidence that haploinsufficiency of TBX1 is likely to be responsible for many of the physical features associated with the deletion. However, although a number of genes have been implicated as possible schizophrenia susceptibility loci, further confirmatory studies are required.