CHARGE syndrome is a multiple anomaly disorder in which patients present with a variety of phenotypes, including ocular coloboma, heart defects, choanal atresia, retarded growth and development, genitourinary hypoplasia and ear abnormalities(1). Despite 70-90% of CHARGE syndrome cases resulting from mutations in the gene CHD7, which encodes an ATP-dependent chromatin remodeller, the pathways underlying the diverse phenotypes remain poorly understood(2). Surprisingly, our studies of a knock-in mutant mouse strain that expresses a stabilized and transcriptionally dead variant of the tumour-suppressor protein p53 (p53(25,26,53,54))(3), along with a wild-type allele ofp53 (also known as Trp53), revealed late-gestational embryonic lethality associated with a host of phenotypes that are characteristic of CHARGE syndrome, including coloboma, inner and outer ear malformations, heart outflow tract defects and craniofacial defects. We found that the p53(25,26,53,54) mutant protein stabilized and hyperactivated wildtype p53, which then inappropriately induced its target genes and triggered cell-cycle arrest or apoptosis during development. Importantly, these phenotypes were only observed with a wild-type p53 allele, as p53(25,26,53,54/-) embryos were fully viable. Furthermore, we found that CHD7 can bind to the p53 promoter, thereby negatively regu-lating p53 expression, and that CHD7 loss in mouse neural crest cells or samples from patients with CHARGE syndrome results in p53 activation. Strikingly, we found that p53 heterozygosity partially rescued the phenotypes in Chd7-null mouse embryos, demonstrating that p53 contributes to the phenotypes that result from CHD7 loss. Thus, inappropriate p53 activation during development can promote CHARGE phenotypes, supporting the idea that p53 has a critical role in developmental syndromes and providing important insight into the mechanisms underlying CHARGE syndrome.