Fetal motor activity is believed to influence umbilical cord growth. As Down's syndrome is associated with hypotonicity and reduced fetal activity, we hypothesized that newborn infants with this syndrome have short umbilical cords. We identified 21 infants with Down's syndrome and compared each individual cord length to mean standard values derived from the same population and matched for sex, race, and gestational age. Infants with Down's syndrome were found to have significantly shorter umbilical cords (mean of 45.1 cm compared with 57.3 cm for matched standards). It is not clear whether their cords are shorter on the basis of decreased fetal activity, genetics, or both. If it is on the basis of decreased fetal activity, it would be interesting to see if those with the shortest cords (presumed to have been the most hypoactive in utero) could be predicted to have worse neurodevelopmental outcomes.