Panic disorder first appeared as a specific diagnostic entity in 1980, in the third Edition of "Diagnostic and Statistical Manual of Mental Disorders" (DSM III). The classical anxiety neurosis was divided into two separate entities: panic disorder and generalized anxiety disorder, whose major criteria for distinction was based, in a simplified manner, on the presence or absence of panic attacks in the patient's history. Validity of the concept of panic disorder as a clinical and autonomous entity is now widely accepted. It is based on numerous epidemiological, phenomenological, biological, genetic and therapeutic studies that have established, that panic disorder may be clearly distinguished from other anxiety and mood disorders. However, this disorder still has unknown aetiology and criteria for definition remain purely clinical. Controversies as regards the validity of diagnostic criteria for panic disorders may account for its successive definitions in the DSM III-R, then in the DSM IV. In fact, in contrast to the definition of panic attacks that has remained practically constant, panic disorder was initially defined by the recurrence of panic attacks. It is now considered by the authors of the DSM IV as a disorder characterized by a chronic anxiety, focused on the risk for panic attacks showing symptoms evocative of autonomic dysregulation. In the DSM IV, panic attack is now considered as a syndrome which is not specific for panic disorder. Panic disorder may be diagnosed in a patient who has suffered from recurrent panic attacks, provided that one at least of the latter have been associated with one of the following symptoms: persisting fear from other panic attacks; concerns about possible implications of panic attacks or their consequences; major behavioural changes related to the attacks. Evolving positions of the successive authors of the DSM contrast with more conservative attitudes of the authors of the CIM 10, who still consider agoraphobia as a key symptom. Whatever the issues of these definitions, it must be kept in mind that panic disorder is a severe syndrome, and leads to major suffering and significant impairment of the patients' quality of life as well as their social life and interpersonal relationships. Comorbidity with depressive and addictive disorders is frequent, and panic disorder is considered by numerous authors as a risk factor for suicide. Due to the severity of panic disorder, its frequency and the fact that it is too often undiagnosed (although there are effective therapeutic strategies), efforts are fully warranted, so that patients may benefit from early diagnosis and adequate treatment.