Marshall-Smith syndrome: A disorder characterized by advanced bone age at birth, broad forehead, prominent eyes, and small chin. There is difficulty feeding, failure to thrive, retarded psychomotor development, and predisposition to respiratory infection. It may be fatal within the first years of life. The cause of the syndrome is unknown. It is named for Richard E. Marshall and David W. Smith who were the lead and last authors, respectively, of the first description of the syndrome in 1971. It shares some features with a condition called Weaver syndrome.