Foetal alcohol syndrome has been described as the commonest preventable cause of mental retardation in the Western world. It refers to a pattern of malformations, growth retardation and central nervous system impairments found in children of mothers who drink large amounts of alcohol while they are pregnant. This paper describes the nature of foetal alcohol syndrome and the related condition of foetal alcohol effect, presents findings from a study of young children in the care of social services in Northern Ireland and discusses the implications for Social Workers working with affected children and families. (Contains 1 table.)