This paper gives an introduction to the psychosocial work in the Swedish Child Health Services (CHS). There are substantial problems in defining and evaluating the preventive mental health work of the CHS. The issues raised include: why early preventive intervention is important; the promotion of parental mental health as an aim of the CHS; how the CHS can increase parenting knowledge and skills; what evidence there is about intervention among target groups; and finally, how recent research knowledge can be applied in the CHS.