We report on a 15-year-old patient with hyperactivity, intellectual disability and severe speech developmental delay. An array CGH analysis revealed de novo 2q34 deletion, 958 kb in size, involving a single protein coding gene ERBB4 (position 212,505,294–213,463,152; NCBI build 36). The ERBB4 gene is important in numerous neurobiological processes in both the developing and the adult brain. The NRG1–ERBB4 signaling pathway has been recently implicated in the pathophysiology of schizophrenia and epilepsy. Many risk haplotypes were identified in several studies across different populations. The severe clinical consequences in our patient demonstrate that the haploinsufficiency of ERBB4 is crucial for intellectual and cognitive function. These observations are compatible with previously reported results. © 2013 Wiley Periodicals, Inc.