Objective: Here we argue for the necessity, validity, and clinical utility of a new diagnostic entity, acute suicidal affective disturbance (ASAD).Method: We expand on the conceptual, clinical, and practical rationale for ASAD, propose its defining features, describe research results to date, and suggest avenues for future research.Results: There is accruing evidence for the existence of a previously unclassified, rapid-onset mood disturbance that geometrically escalates and regularly results in life-threatening behavior.Conclusions: ASAD research may not only improve the field's understanding of suicidal behavior but also enhance clinical effectiveness and save lives.The first step in wisdom is to know the things themselves… objects are distinguished and known by classifying them methodically and giving them appropriate names. (Carolius Linnaeus).Consider the following scenario, based on actual cases encountered by the senior author: an individual is diagnosed with a nonmood disorder psychiatric condition (e.g., schizophrenia) and admitted to inpatient psychiatry. During hospitalization, mood disorder symptoms and suicide risk are regularly assessed and viewed as minimal. The patient's chart indicated the occurrence of a suicide attempt approximately 4 years before. However, the circumstances surrounding this attempt were not documented, and unbeknownst to unit clinicians and unreported by the patient, a past history of rapidonset, intense suicidal crises occurred about 5 years previously. The condition is aggressively treated and clear improvement is observed. The individual is, thus, discharged; approximately 18 hr postdischarge, suicidality again intensifies dramatically, culminating in the individual's death by suicide. The primary condition had not worsened.