In response to the perceived over-diagnosis of pediatric DSM bipolar disorder, acknowledgment that the "classic" adult bipolar phenotype does occur in prepubertal youth, and increased recognition that SMD is a distinct behavioral and/or biological syndrome, the DSM-5 Child Disorders Workgroup proposed a new diagnostic category named temper dysregulation disorder with dysphoria (TDD). Criteria for TDD were largely based on SMD, however, the requirement for hyperarousal was removed and minor changes were made in age of onset and exclusion criteria. Unlike SMD, TDD lacks any demonstrated scientific basis or history of prior research. As such, it seems prudent at this time to continue research on the better-established SMD category with an expectation that any information derived will have ready applicability as work on TDD progresses.