The aim of this scientific research is to investigate how social workers in social service agencies that are determined to work in line with the critical appraisal model make decisions on treatment methods for adolescents with substance abuse disorder. The research is also intended to investigate the challenges involved in the implementation of evidence-based practice (EBP). It is a qualitative study with semi structured interviews. The study results reveal that social workers in Sweden do provide evidence-based treatment methods for adolescents with substance abuse disorder but they do not go through scientific research before deciding on treatment methods for clients. The National Board of Health and Welfare National guidelines (socialstyrelsens nationella riktlinjer) suggest evidence-based treatment methods for social work practitioners and all they need to do is to select treatment methods that match the needs of clients from a list of evidence-based treatment methods. The study also reveals that case officers make decisions on treatment methods for clients but therapists must not implement the treatment methods if they do not find it useful for clients. In addition, Swedish social workers to a greater extent are provided with resources that can lead to a successful implementation of evidence-based practice. Out of seven participants in the current study, only one participant mentioned lack of financial resources as an obstacle to the provision of evidence-based training to social workers in the institution where he works.