Histologic evaluation of the larynx in sudden infant death syndrome. Seventy-four larynges removed at death from children who died of sudden infant death syndrome (SIDS) have been studied by serial sectioning in the transverse plane. An increase in subepithelial glandular tissue is seen in many specimens, and the reduction in the available subglottic area has been measured with the Measuremouse Image Intensifying system. This preliminary report confirms that in some of these children with SIDS, particularly around the age of 3 months, there is a potentially lethal reduction in subglottic airway secondary to an increase in mucus-secreting glands, possibly from an associated mild upper respiratory tract infection. Accepting that adequate control infants within this age group who have not had any trauma to the laryngotracheal area are not available, these findings offer a possible explanation for what are always tragic events. 