ADHD is the most common psychiatric disorder of childhood. It is considered to be a neurodevelopmental disorder that may persist from chilhood into adulthood. In childood it is associated with several outcomes such as inattention, hyperactivity and impulsivity. Symptoms may change as a person gets older with an increased risk of developing psychiatric comorbidities such as depression, anxiety and substance addiction. However, recent studies diverge from the traditional perspective. These authors hypothesized that ADHD may appear in adulthood, not as a continuation of child ADHD, but some limitations have to be considered. Firstly, ADHD often goes unrecognized throughout childhood. Secondly, families may help the children to develop compensation strategies and adaptative behaviors. The purpose of this report is to better investigate these different and innovative clinical results and understand if adult ADHD could really be considered as a distinct, different pathology, as a late-onset disorder. We conducted a brief review of literature and included the most recent scientific longitudinal follow-up cohort studies. We conclude that, while adult ADHD is still considered a continuation from childhood, many questions of late-onset ADHD remain and further research is necessary to better understand and explain the etiology, the development, the clinical impact, and the psychotherapeutic and pharmacologic treatment of this late-onset disorder.