The external arcuate nucleus (EAN), located in the ventral medulla, is studied in 24 infants dying of sudden infant death syndrome (SIDS) and 15 age-matched controls to identify differences in morphology in this region, thought to be involved in respiratory regulation. Significant differences are noted in EAN neuronal density, percentage of back-to-back neurons and volume of the EAN relative to the adjacent pyramids. These changes may be useful in evaluating sudden infant death.