A retrospective study of the clinical literature of fetal alcohol syndrome (FAS) was conducted to determine the incidence of FAS among younger and older siblings of a patient with FAS. The incidence of the disorder among older sibs was 170 per 1,000 whereas among younger sibs the incidence was 771 per 1,000. Since the risk for FAS in the general population is 1.9 per 1,000, these results clearly indicate the high risk of FAS among siblings if one sib is diagnosed as FAS.