Children and young people with untreated mental health disorders can develop chronic disorders and severe somatic diseases later in life. The right treatment at the right time is therefore important to promote good mental health. Healthcare personnel are required to follow national guidelines, and high-quality guidelines are thus important for patient safety. We wanted to assess the quality of Norwegian national guidelines for the treatment of mental disorders in children and young people and compare these with corresponding guidelines in Sweden and Denmark. We conducted manual searches in the relevant national health authorities’ websites and selected five Norwegian guidelines (treatment of ADHD, bipolar disorders, psychosis, suicide and eating disorders), three Danish guidelines (ADHD, anorexia and bulimia) and one Swedish guideline (ADHD). For the purpose of quality assessment, we used an internationally recognised checklist (AGREE II), on which Norwegian guidelines must be developed in accordance with the Norwegian Directorate of Health’s own guide for developing guidelines. The checklist consists of 23 items divided into six domains: scope and purpose, stakeholder involvement, rigour of development, clarity of presentation, applicability, and editorial independence. We found that the overall quality of the Danish and Swedish guidelines was very high and met most of the 23 criteria organised within six domains. The Norwegian guidelines met the criteria for scope and purpose and stakeholder involvement, but had major shortcomings in terms of rigour of development, clarity of presentation, applicability, and transparency of editorial independence. Keywords: evidence-based practice, national guidelines, children and adolescents, mental disorders