Background: Dysfunctional breathing (DB) is a respiratory disorder involving an upper chest breathing pattern and respiratory symptoms that cannot be attributed to a medical diagnosis. Aim: The overall aim of this thesis was to describe patients with DB and investigate clinical outcomes after physiotherapy treatment. Methods: Study I was descriptive and comparative, that included 25 patients with DB and 25 age- and sex-matched patients with asthma. Health-related quality of life (HRQoL), anxiety, depression, sense of coherence, influence on daily life due to breathing problems, respiratory symptoms, emergency room visits and asthma medication were investigated. Study II, a 5-year follow-up study based on the same sample as study I (22 patients with DB, 23 patients with asthma), studied treatment outcomes after information and breathing retraining. Study III was descriptive and correlational (20 healthy subjects), investigating whether the Respiratory Movement Measuring Instrument (RMMI) can discriminate between different breathing patterns in varying body positions. Study III also studied correlations between respiratory movements and breathing volumes (12 healthy subjects). Study IV was a single-subject AB design with follow-ups. Self-registered patient-specific respiratory symptoms and respiratory-related activity limitations and breathing pattern (measured with the RMMI) were evaluated after an intervention consisting of information and breathing retraining in five patients with DB. Results: Patients with DB had lower HRQoL (SF-36): vitality (mean 47 vs. 62), social functioning (70 vs. 94) and role emotional (64 vs. 94) (p<0.05) than patients with asthma. The DB group had a higher prevalence of anxiety (56% vs. 24%) and experienced more breathing problems than the asthma group. Patients with DB had made several emergency room visits and had been treated with asthma medication. At the 5-year follow-up, patients with DB showed improved HRQoL (SF-36): physical function 77 to 87 (p=0.04), decreased breathing problems and emergency room visits, and they were not treated with asthma medication. The RMMI can differentiate between different breathing patterns in different body positions. Strong correlations between respiratory movements and breathing volumes were observed (rs 0.86-1.00). The results in study IV indicate that patients with DB benefit from information and breathing retraining regarding decreased respiratory symptoms and activity limitations and improved breathing pattern.