Smith-Magenis Syndrome (SMS) is a complex, pediatric, neurobehavioral, contiguous gene syndrome ascribed to interstitial microdeletion of chromosome 17, band 11.2. The syndrome is characterized by distinctive behavioral, neurocognitive, and neuropsychiatric abnormalities. This genetically mediated disorder of mental retardation prompts behavioral researchers to examine the links between genes, brain, and behavior in order to solve the gene-behavior puzzle and the genotype/phenotype correlation. In this article, the authors review literature on behavioral profile and its associated psychopathologies, cognitive profiles, multisystem abnormalities, and genetic correlates that highlight the complexities of the disorder.