Abstract

Severe irritability is a common reason for referral to child mental health services, yet its diagnostic boundaries and clinical implications remain unclear. This thesis examines the relatively new child mental health diagnosis Disruptive Mood Dysregulation Disorder (DMDD) in a Norwegian outpatient population, focusing on its prevalence, clinical correlates, parental stress, and its distinction from ICD-11 Oppositional Defiant Disorder with chronic irritability (ODD-CI). DMDD was found to be highly prevalent, with nearly 25% of children referred to specialized outpatient services fulfilling diagnostic criteria, and was associated with marked functional impairment, high symptom burden, and substantial family stress. Parenting stress was strongly linked to child regulatory difficulties, while comparisons with ODD-CI revealed substantial symptom overlap but greater emotional dysregulation in DMDD. Overall, the findings suggest that DMDD represents a severe manifestation of chronic irritability with significant impact on children and families, underscoring the need for early identification and targeted interventions.