There is a growing appreciation that clinically impairing irritability is an important transdiagnostic symptom among children and adolescents with mental illness. Severe irritability, defined by frequent, developmentally inappropriate temper outbursts and low frustration tolerance, is one of the most common reasons that youths are referred for psychiatric evaluation and care.¹ Although chronic irritability is the primary symptom in disruptive mood dysregulation disorder, the symptom is common in a diverse set of DSM-5 diagnoses, including major depressive disorder, autism spectrum disorder, oppositional defiant disorder, bipolar disorder, and generalized anxiety disorder.¹ Given that clinically impairing irritability is often predictive of poor outcomes in childhood and worse clinical course in adulthood, a concerted effort is being made to refine the definition of this symptom and determine if severe irritability could be better understood and treated as an independent diagnosis.¹