Four recent studies may have turned what we know about attention-deficit/hyperactivity disorder (ADHD) on its head. By following large cohorts from early childhood to adulthood, they claim to have discovered that ADHD can start in adults who did not have the disorder before the DSM-5 cutoff of 12 years. However, before we rewrite the DSM and start prescribing stimulants to every adult who cannot concentrate, it is important to take a closer look at this research.