The Disruptive Mood Dysregulation Disorder (DMDD) was included for the first time in the 5th Revision of the DSM. A transatlantic controversy surrounding the clinical picture and prevalence of early-onset bipolar disorder gave the occasion to develop a new diagnostic category in the chapter "Depressive Disorders" capturing a behavioral phenotype of non-episodic, chronic irritability and frequent temper tantrums. The present paper reviews the first available studies applying the new criteria. While DMDD can be clearly distinguished from bipolar disorder, preliminary evidence suggests a strong overlap with oppositional-defi ant disorders (ODD). For the upcoming revision of the ICD it should be discussed to introduce a specifier indicating whether or not the presentation of ODD includes chronic irritability and anger, rather than establishing a new diagnosis. Regardless of the nosological categorization of the described behavioral phenotype main challenges represent a better understanding with regard to its etiology, developmental psychopathology and prognosis and the development of beneficial treatment options.