This article presents the evaluation of one of these programs - the Prejop prevention experiment in the Hague. Relevant aspects of the method of assistance used in this programme are: early detection of juveniles 'at risk' by detectives of the juvenile police in close collaboration with social workers of the prevention programme, start of social assistance directly after the police contact, quick referral to a branch of the mental health system most capable of handling the problems at hand. For Dutch juveniles the programme reduced family malfunctioning, delinquent behavior and the amount of returns to police notice. For juveniles from ethnic minorities the programme was less beneficial. It is concluded that early social welfare intervention is a promising perspective in the area of delinquency prevention. (Author abstract)