This study examines the etiology of antisocial behaviour and explores the biological and environmental factors which influence its development. The aim of this research is to look at whether early detection of severe problem behaviour in children, coupled with appropriate intervention, may prevent the possibility of antisocial behaviour patterns firmly established during the adolescent years. Using the framework of an ecological model this study examines the various layers at which behaviour is influenced. Social policy reforms in New Zealand during the past fourteen years (1984-1998) are outlined and the impact they have had upon families and social work practice within the Children, Young Persons and their Families Service (CYPFS). The policy and procedural changes within CYPFS are evaluated. Current literature on antisocial behaviour, treatment, interventions and prevention, post traumatic stress disorder and attachment, is reviewed. This is an exploratory research design and uses the method of file content analysis to examine 306 retrospective case records which were referred to a local CYPFS office between 1990-1995, under the category of Problem Behaviour. The findings from this study are related to the wider context of research in the literature. There was an over representation of Maori within the study sample, compared to the Maori population from the local community. here were marked gender differences for behaviour categories, with an over representation of males in the severe antisocial behaviour accompanied by recidivism and recidivist offending only categories and an over representation of females in the adolescent/peer related behaviours. Children and young people who fared the worst came from families with multiple problems and environments where there was domestic violence and child abuse. One third of the young people from this study had severe antisocial behaviour and/or recidivism. Most of them did not receive an early or timely intervention and many placements, estimated to be costly to CYPFS. The overall findings from this study suggest that a timely intervention on the first referral to CYPFS may have prevented ongoing re-referrals and costly placements. Further research is recommended in order to test these findings.