Cornelia de Lange Syndrome (CDLS) is a rare multiple congenital anomaly syndrome. Etiology is still unknown. Clinical diagnosis of CDLS mainly depends on the recognition of distinctive facial appearances. Major characteristics include developmental delay, growth retardation, hirsutism, limbs anomalies and specific facial features. This article presents a case of 12-year-old girl with Cornelia de Lange Syndrome. Before applying any dental treatments, the dentist has to evaluate the cardiac condition as well as coagulation condition of the patient. Due to mental retardation of the patient, behavior management is also a challenge.