The first familial observation of the Marshall-Smith syndrome is showed. The propositi are a male and female relatives with a double consanguinity and whose family comes from a small area with a high rate of inbreeding. According to this hypothesis autosomal recessive inheritance for this syndrome is proposed as very suggestive. These two new cases seem to prove that the mental retardation may not be a typical clinic features and that survival of the cases longer that expected may be considered. One of our patients is a three years old female and the other one is nearly eleven years old male. The syndrome delineation is given by very closely homogeneous patterns. Said patterns also single it out from the Weaver syndrome.