According to its initial definition, which dates back more than 50 years, a transient ischemic attack (TIA) is a sudden focal neurologic deficit lasting for less than 24 hours, of presumed vascular origin, and confined to an area of the brain or eye perfused by a specific artery. Recent data on the pathophysiology of cerebral ischemia and the progress made by the imaging techniques have led an American TIA Working Group to propose a new definition which states that: "A transient ischemic attack is a brief episode of neurologic dysfunction, caused by local brain or retinal ischemia, with clinical symptoms typically lasting less than one hour, and without evidence of cerebral infarction". The advantages and limitations of this new definition, the need for an emergency medical care in the presence of a TIA, the clinical signs associated with this condition, the diagnostic work up, and the differential diagnosis are briefly discussed. A clinical example illustrates the difficulties that can be encountered in a case of TIA.