Cornelia de Lange syndrome is a dysmorphogenic disorder characterized by multiple congenital abnormalities, mental retardation, growth retardation and neurodevelopmental abnormalities. Diagnosis for the Cornelia de Lange syndrome is dependent on the clinical observation because neither definite biological marker nor definite chromosomal abnormality have been investigated. Clinical observation is important for the diagnosis, so we report a case of Corenelia de Lange syndrome with mental retardation and autistic disorder. The patient is a 6-year old girl. Her motor development and language development have been delayed. She could say no meaningful word and understood simple command partially. She showed poor eye contact and poor emotional int...