In order to examine the predictive value of risk factors for the Sudden Infant Death Syndrome (SIDS), we have interviewed the parents of 80 SIDS victims and 80 parents of a healthy control group. From these interviews a list of 24 clinical and behavioural symptoms was assembled which appeared to be associated with the risk for SIDS. Out of this list of 24 symptoms the average number of symptoms reported to be observable in SIDS victims was twice as large as the average number of symptoms reported for healthy controls. The following symptoms appeared markedly more often in SIDS victims than in the controls: difficulties in awakening the baby, shrill crying, apathy, few movements during sleep, and cyanosis. We have attempted to consider a possible bias in the report of the parents of deceased infants by the introduction of an "exaggeration factor". By application of Bayes' theorem the highest predictive probability, 2.7%, was found for difficulties in awakening the baby. This is approximately nine times the assumed a priori probability of SIDS of 0.3%. We conclude that behavioural risk factors have a low but still remarkable predictive probability. A behavioural pattern of apathy and sleepiness indicates risk with a high probability.