The DSM-5 ADHD and Disruptive Behaviors Work Group proposed two major changes for diagnosis of attention deficit hyperactivity disorder (ADHD) in adults: (1) inclusion of four new impulsivity symptoms and (2) reduction in the number of symptoms required for assigning an ADHD diagnosis. In this case-control study, the performance of these modifications was assessed in a clinical sample of 133 adult subjects (68 ADHD cases and 65 non-ADHD control subjects). The proposed new impulsivity symptoms for adults do not improve ADHD diagnosis enough to overcome potential negative effects of changing the criteria. However, fewer symptoms than the six-of-nine threshold required by DSM-IV provided the best cutoff point for identifying adults who are impaired.