In 40 to 60% of children with ADHD, the disorder persists into adulthood. Nevertheless, diagnosis in adulthood sometimes becomes a challenge because, even the etiology is not very clear yet, ADHD shares several clinical features or may coexist with other psychiatric disorders. This issue leads to confusion and also to a delayed treatment or a wrong treatment, causing negative effects on patient outcomes.

To highlight the importance of making an accurate differential diagnosis and to consider the coexistence of other mental disorders, in the diagnosis of a patient with ADHD.

Systematic review of the literature in English (Pubmed). Keywords: “adult ADHD”; “bipolar disorder”; “substance abuse”; “personality disorders”.

Adult ADHD has a prevalence in Europe of 3,4% and it seems to appear more frequently in developed countries. In adults, the clinical presentation differs from children. There often are symptoms of impulsivity, attention deficit, restlessness, and emotional dysregulation and risk behavior, causing difficulties in everyday functioning. The coexistence of substance abuse and the similarity between bipolar disorder and personality disorders with ADHD, translate in a difficult diagnosis, especially for patients with mild presentations.

So far, the authors conclude that a detailed clinic history plus the validated scales for adult ADHD are the most reliable tools for diagnosis. Neuroimaging and EEG studies do not provide conclusive data to consider them as diagnostic methods.