Rubinstein-Taybi Syndrome was first described in 1957 but only in 1963 as a distinguishable type of moderate mental retardation. The cause is still unknown although some type of genetic origin is possible. No consistent chromosomal abnormality has been demonstrated, the chromosomal analysis is normal, and cases are generally not considered hereditary. The recurrent risk for siblings is approximately 0.1% but may be as high as 50% for offspring of patients with the syndrome. The Rubinstein-Taybi syndrome is not at present detectable before birth and is evenly found in both males and females. The syndrome was thought to be rare but an increase in the number of reported cases each year suggests it is not as rare as estimated. It is thought to occur in about 1 in 300,000 births, and since it has become readily identifiable, more than 400 cases have been reported worldwide.