Infants with mandibular hypoplasia are at risk of sudden death from cardiorespiratory arrest secondary to upper airway obstruction. To evaluate diagnostic difficulties that may occur at autopsy in such infants, the autopsy files at the Adelaide Children's Hospital (ACH) for 36 years, 1959 to 1994, were reviewed. Eight cases were identified (age range, 2 days to 10 months; mean age, 2.2 months; male/female ratio, 5:3). In all cases, death was considered most likely due to airway obstruction related to mandibular hypoplasia or its treatment. Although death occurred in the hospital in five cases, one infant suddenly collapsed at home while feeding and died, and two infants were unexpectedly found dead in their cribs at home. Three infants had defined genetic syndromes. Although all the infants had histories of antemortem airway obstruction, one infant had normal oxygen saturation studies before hospital discharge, and one infant had a tracheostomy. Acute bronchopneumonia was an exacerbating factor in one case. Assessment of mandibular size is important in any infant who dies unexpectedly; and if hypoplasia is found, careful review of the clinical details for evidence of airway obstruction is necessary to help distinguish these cases from sudden infant death syndrome (SIDS). Sudden death may, however, occur in infants with mandibular hypoplasia in spite of apparent clinical stability before death with no significant recent episodes of oxygen desaturation.