The proposed revision of the diagnostic criteria in DSM-5 for attention-deficit/hyperactivity disorder (ADHD) will not fundamentally change the concept of ADHD. This is mainly due to the fact that, DSM-5 will retain the exact DSM-IV wording of all 18 symptoms, but will add new examples that make the criteria more appropriate for children, adolescents and adults. The age of onset will also be changed from 7 to 12 years, the subtyping of the disorder will change, and pervasive developmental disorders will no longer be an exclusion criterion. Although the main concept is unchanged, the suggested changes will most likely increase the prevalence of ADHD, especially in adults and adolescents, but maybe also in children. The added examples will also result in necessary revisions and new validations of rating scales and diagnostic interviews. This review will examine each of the proposed DSM-5 changes and the impact they may have, and in addition, the paper will make an overview of the main characteristics of some of the international and national guidelines for assessment and treatment of ADHD and how these impact the clinical practice.