Attention-Deficit/Hyperactivity Disorder (ADHD) is one of the most common mental disorders worldwide. Given the children and adolescents individual needs, it is essential to understand this disorder in its characterization, etiology and treatment. This literature review intends to systematize and organize the best scientific evidence about this disorder, including characterization, epidemiology, diagnosis and treatment. A bibliographic research was carried out within Scopus, Scielo, Pubmed, Web of Science databeses as well Google Scholar, and the INFARMED website has been consulted. The research was carried out by using the combination of keywords: Attention-Deficit/Hyperactivity Disorder, etiology, diagnosis, comorbidities, psychotropic medication and non-pharmacological treatment. Scientific studies were selected between the years 2003 and 2021, as well as studies in Portuguese and English. It was found that beyond the importance of an early diagnosis, it is importante to identify the presence of comorbidity too, in order not to deteriorate the disease prognosis. Scientific advances have demystified the etiology of ADHD resulting from factors related to diet, being mainly attributed to the genetic component. The pharmacological treatment is mainly performed with psychotropic medications, but the institution of a nonpharmacological treatment proved to be extremely important, concomitantly, to be more effective and safe. It was concluded that it is extremely important to continue to carry out studies in order to improve the diagnosis criteria and the guidelines for establishing the pharmacological treatment, with a view to a personalised treatment for each child or adolescent. [ABSTRACT FROM AUTHOR]