The term 'breathing exercise or re-training' has numerous interpretations depending on the nature of the therapy, therapist and cultural background. The objective of this review was to assess the evidence for the effectiveness of breathing retraining for patients with asthma. Due to the small number of studies meeting the criteria for inclusion into this review, the small number of patients in the studies and the use of diverse interventions in the included studies, no reliable conclusions can be drawn as to the beneficial effects of breathing retraining in asthma. However with the introduction of two further studies trends for improvement in an increased number of outcomes were found. There is therefore a need for large scale trials involving breathing retraining in order to observe its effectiveness in the treatment and management of asthma.