The prevalence of attention-deficit/hyperactivity disorder (ADHD) has been increasing, and the growing number of people with this disorder, especially the non-pediatric population, get prescriptions for this condition. However, controversies are also growing around this disease. To provide optimal treatment to a patient presumed to have adult ADHD, it is crucial to understand the implications of diagnosing and treating adult ADHD. In this article, we proposed a critical review on the concept of ADHD from various points of view and suggested the diagnostic and therapeutic implications of adult ADHD. This article will serve as a small cornerstone for a valid diagnosis and a proper treatment of ADHD, especially in the adult population.