AbstractBackground.A growing body of research suggests that deficient emotional self-regulation (DESR) is common and morbid among attention-deficit/hyperactivity disorder (ADHD) patients. The main aim of the present study was to assess whether high and low levels of DESR in adult ADHD patients can be operationalized and whether they are clinically useful.Methods.A total of 441 newly referred 18- to 55-year-old adults of both sexes with Diagnostic and Statistical Manual of Mental Disorders: Fifth Edition (DSM-5) ADHD completed self-reported rating scales. We operationalized DESR using items from the Barkley Current Behavior Scale. We used receiver operator characteristic (ROC) curves to identify the optimal cut-off on the Barkley Emotional Dysregulation (ED) Scale to categorize patients as having high- versus low-level DESR and compared demographic and clinical characteristics between the groups.Results.We averaged the optimal Barkley ED Scale cut-points from the ROC curve analyses across all subscales and categorized ADHD patients as having high- (N = 191) or low-level (N = 250) DESR (total Barkley ED Scale score ≥8 or