Introduction: Sudden intrauterine death syndrome (SIUDS) and sudden infant death syndrome (SIDS) are often associated in a single pathology, resulting from an unexpected fetal or infant injury. Among the various causes, the action of external toxics, still current in the West, should not be excluded. The present histopathological observations indicate the brainstem nuclei as possible neuronal targets of toxic substances; these cause direct damage to cells, including those at the mitochondrial level, as well as indirect functional impairment. During fetal life in utero, the placenta does not act as a total filter; rather it proves permeable to toxics which are able to penetrate the hematoencephalic barrier which shields the fetus. Clinical tests have yet to be devised which reliably signal impending danger of unexpected fetal or infant injury from external toxics.