The facilities provided by youth advisory services are not really original, because services existing before 1970 already provided most of the facilities and utilized the same methods. The innovation of the services exists more in the way they approach young people. The effect of the services has been to increase the number of assistance posts in areas of social turmoil, thereby making it easier to carry out on-the-spot tracing and diagnosis of behavioral disturbances or social handicaps. The originality of this approach has been in a breaking down of hierarchical structures which is not in line with the sectoral concept of mental health services, but which brings assistance, reception and treatment networks to areas not properly covered. Scientific evaluation of the preventive work by the wide range of youth advisory services seems to face the same continuing problem encountered in all preventative research. The basic problem exists in defining the very notion of success, because that definition requires that the chief criteria be separated out from a multitude of variables. Attendance figures still convey an idea of the success of the services. There is nothing to show that long-lasting institutions interest the young. (BN)