We surveyed 64 individuals with the diagnosis of Brachmann-de Lange syndrome (BDLS) to determine the natural course and cause of the disorder. The 64 individuals were ascertained through membership in a national organization, the Cornelia de Lange Syndrome (CDLS) Foundation, comprised of families who have a relative with BDLS. We surveyed 64 families by questionnaire and personally examined 24 of the 64. Our data suggest that lower birth weight correlates with a more severe phenotype, specifically including severe upper limb malformations and greater psychomotor retardation. The lower birth weight group showed a significant excess of females. The miscarriage rate was normal and there were no recurrences reported in the 64 families we surveyed. Major management problems included feeding problems and projectile vomiting, behavioral problems including frequent tantrums, hearing and dental difficulties, and recurrent respiratory tract infections. The oldest, teenaged subjects in our study entered puberty; although pregnancy has not been reported in the syndrome, it is likely that people with BDLS are fertile. Though most BDLS children reared at home survive through adolescence, a significant degree of psychomotor retardation and difficult medical management problems still occur.