Objectives : In the Diagnostic and Statistical Manual of Mental Disorders, 5^th edition (DSM-5), children with severe nonepisodic irritability are diagnosed as disruptive mood dysregulation disorder (DMDD) and this diagnosis is included in the mood disorder section. The current study aimed to know whether the DMDD is a subgroup of bipolar disorder (BD) or an independent disorder. Method: For gathering valid English and Persian data, Medline, PsycINFO, Scopus, and DSM databases for English and SID for Persian resources were searched and reviewed until Summer of 2013. Results: Up until now research comparing severe and permanent (nonepisodic) irritabilities (equivalent to DMDD) with BD indicate that BD and DMDD are similar in severity and functional impairment, and different in gender distribution, familial clustering, course and prognosis, comorbidities and neuropsychophysiologic functions. In following years, children with DMDD are more likely to suffer from unipolar depressive and anxiety disorders, but BD has not been seen among them. Conclusion: The DMDD seems not to be a subgroup of BD and rather it should be included as an independent diagnosis in the mood disorder section. The DSM editors need to be flexible enough to make necessary revisions encountering further new findings.