Sudden infant death syndrome remains the leading cause of death in infants between the ages of 1 month and 1 year. Diagnosis at autopsy is usually reached by process of elimination, as no obvious cause of death is recognized. The larynges of 23 sudden infant death syndrome victims, as well as 6 infants and 3 fetuses who died of other known causes, were examined in this study. While thickening of the basement membrane of the vocal cords was apparent in all sudden infant death syndrome victims, no such finding was present in the larynges of infants and fetuses dying of other causes. Thus, it is suggested that basement-membrane thickening may serve as a diagnostic tool for identification of sudden infant death syndrome at autopsy.