Hyperventilation is defined as breathing in excess of the metabolic needs of the body, eliminating more carbon dioxide than is produced, and, consequently, resulting in respiratory alkalosis and an elevated blood pH. The traditional definition of hyperventilation syndrome describes "a syndrome, characterized by a variety of somatic symptoms induced by physiologically inappropriate hyperventilation and usually reproduced by voluntary hyperventilation". The spectrum of symptoms ascribed to hyperventilation syndrome is extremely broad, aspecific and varying. They stem from virtually every tract, and can be caused by physiological mechanisms such as low Pa,CO2, or the increased sympathetic adrenergic tone. Psychological mechanisms also contribute to the symptomatology, or even generate some of the symptoms. Taking the traditional definition of hyperventilation syndrome as a starting point, there should be three elements to the diagnostic criterion: 1) the patient should hyperventilate and have low Pa,CO2, 2) somatic diseases causing hyperventilation should have been excluded, and 3) the patient should have a number of complaints which are, or have been, related to the hypocapnia. Recent studies have questioned the tight relationship between hypocapnia and complaints. However, the latter can be maintained and/or elicited when situations in the absence of hypocapnia in which the first hyperventilation and hypocapnia was present recur. Thus, the main approach to diagnosis is the detection of signs of (possible) dysregulation of breathing leading to hypocapnia. The therapeutic approach to hyperventilation syndrome has several stages and/or degrees of intervention: psychological counselling, physiotherapy and relaxation, and finally drug therapy. Depending on the severity of the problem, one or more therapeutic strategies can be chosen.