Little neuropathology has been documented in sudden infant death syndrome (SIDS) infants. Two hypotheses predict abnormalities in the hypoglossal nucleus and dorsal motor nucleus of the vagus: first, that upper airways are obstructed as a result of abnormal innervation (principally the hypoglossal nerve), and second, that they are obstructed as a result of abnormal cardiorespiratory control (the vagus nerve). A quantitative morphometric analysis was carried out to test these hypotheses in SIDS infants and controls (who died in accidents). The following nuclei dimensions were analyzed; length, volume, density, and estimated total cell number. In addition, cell size was analyzed. There were no differences in the anatomical distribution, site, or number of neurons between the groups. The most significant difference between the SIDS and control infants was the neuronal size: control infants had significantly larger neurons. In many other variables, there were trends suggesting a difference between the groups: the volume occupied by the neuronal populations was smaller in the SIDS infants, and therefore the neuronal density was increased. These values suggest differences in the development of these nuclei between SIDS and control infants.