The concept of hyperventilation and the principle of a vicious circle provide an elegant explanation for the development of a wide range of somatic and psychological symptoms, the so-called hyperventilation syndrome (HVS). The model has a high degree of credibility and has led to the development of therapeutic interventions that appeared beneficial. However, recent investigations dismiss hyperventilation as an important symptom-producing mechanism. First, the hyperventilation provocation test appears to be invalid as a diagnostic test. Second, studies using ambulant monitoring of pCO2 demonstrate that the vast majority of real-life attacks are not attended by decreases in pCO2. Third, the evaluation of therapy outcome studies indicate that the beneficial effect of breathing retraining is probably not mediated by reducing the tendency to hyperventilate. We conclude that a diagnosis of HVS should be avoided.