A retrospective study was made of the behavioral patterns of 46 infants whose deaths were attributed to the sudden infant death syndrome. Controls were the victims' siblings. Data concerning the infants' behavioral pattern were collected retrospectively from the parents, utilizing a modification of the Carey temperament questionnaire. The parents' recollection of the victims indicated that they: (1) had less intense reactions to environmental stimuli, (2) were less active physically, (3) were more breathless and exhausted during feeding, and (4) had more abnormal cries. The behavioral characteristics had a positive correlation with various postmortem evidences of antecedent chronic hypoventilation and hypoxemia. It would be a serious error for any parent to be told that their infant was at risk based on the behavioral pattern reported retrospectively by parents of victims of SIDS, because the pattern is also a common one in other infants.