Smith-Magenis syndrome is caused by a 17p11.2 deletion. It associates mental retardation, facial dysmorphism and brachydactyly; aberrant behavior and major sleep problems are present in 70% of the cases. It is probably under-diagnosed because the facial abnormalities are mild and the behavioral problems with hyperactivity and self-injuries are dominant, leading to the diagnosis of psychiatric pathology. However these behavioral problems are sufficiently characterized to allow the diagnosis of the syndrome and look for a 17p11.2 microdeletion. Otorhinolaryngologic, ophthalmologic, cardiac and renal abnormalities can be associated and their evaluation is necessary. Smith-Magenis syndrome is considered as a contiguous gene syndrome. Genes have been mapped and isolated to the critical region, but their participation in the pathogenesis of the syndrome remains unclear.