Smith Lemli Opitz Syndrome (SLOS) is an autosomal recessive cholesterol biosynthesis defect which is characterized by both multiple kongenital anomaly and mental retardation. It is the protype of inherited cholesterol metabolism disorder. The main metabolic defect is reduced level or activity of 3-betahydroxysteroid-delta 7-reductase enzyme due to mutations of the related gene. This metabolic defect causes decreased cholesterol and increased 7-dehydrocholesterol levels. In this article, we present the first Turkish patient who is both biochemically and genetically diagnosed as suffering the SLOS with mild clinical symptoms like non Y shaped syndactily, mental retardation, microcephaly. In summary, it is necessary to evaluate mental retardation cases with very few minor findings like 2-3 syndactyly, because SLOS is estimated a relatively common disorder. Copyright © 2010 by Türkiye Klinikleri.