Daily in the UK, frontline medical and paramedical staff are required to manage patients with "collapse ?cause". This universal colloquialism refers to patients who have had an abrupt loss of postural tone. Some of these patients would have had a "blackout" or a transient loss of consciousness (T-LOC). The three most important causes of T-LOC are syncope, epilepsy and psychogenic blackouts. Determining the correct cause is an important challenge; if the initial clinical diagnosis is wrong, investigations may be misdirected, and the final diagnosis and treatment incorrect. Syncope is much more common than epilepsy and may present with symptoms akin to the latter. This fact is not well appreciated and often leads to misdiagnosis. This article deals with the clinical features of the three main causes of blackouts, the value of investigations in arriving at a diagnosis and the problem of misdiagnosis. Pathways for managing patients presenting with blackouts are suggested.