DSM-5 included a new diagnosis, disruptive mood dysregulation disorder, which was added “in order to address concerns about the potential for the overdiagnosis of and treatment for bipolar disorder in children” (1). Diagnostic criteria for this diagnosis require severe temper outbursts, on average three or more times per week, irritable mood most of the day nearly every day, and never having had a distinct period of 1 day or more meeting full criteria (other than the duration criteria) for a manic or hypomanic episode. This diagnosis arose from previous work of a single group that proposed a similar but somewhat different syndrome, severe mood dysregulation, which additionally requires the presence of hyperarousal symptoms not required in the criteria for disruptive mood dysregulation disorder (4, 5). Because of the limited data available, the inclusion of this new diagnosis in DSM-5 has been contentious. A recent examination of disruptive mood dysregulation disorder in previously collected epidemiologic samples (6) found rates to be 3.3% in a preschool sample and 1.1% and 0.8% in two samples of older youths. In those samples, most youths with disruptive mood dysregulation disorder had other comorbid psychiatric disorders, particularly oppositional defiant disorder (odds ratio range, 63–103). The DSM-5 field trials found modest test-retest reliability of disruptive mood dysregulation disorder (kappa=0.25, judged to be in the “questionable” range) (7), although this was similar to the kappa of 0.28 found for major depressive disorder in the same trials. While the criteria for disruptive mood dysregulation disorder were broadly based on those for severe mood dysregulation, there is substantial nonoverlap between youths identified by these two different syndromes.