The aim of this article is to provide an in-depth description of early development in a young child with Smith-Magenis syndrome (SMS). SMS is a multisystem, neurodevelopmental genetic disorder associated with mental retardation that predisposes individuals to a distinct pattern of maladaptive behaviors and other neuropsychological impairments. While there is some research describing outcomes for individuals with SMS in middle childhood, adolescence, and young adulthood, very few descriptions of early development are available in the literature.