The beneficial effects of high-altitude treatment in asthma have been attributed to allergen avoidance. Recent evidence shows that this treatment also improves airway inflammation in nonallergic patients. We hypothesised that high-altitude treatment is clinically equally effective in patients with severe refractory asthma, with or without allergic sensitisation. In a prospective observational cohort study, 137 adults with severe refractory asthma (92 with allergic sensitisation), referred for high-altitude (1,600 m) treatment in Davos, Switzerland, were consecutively included. We measured asthma control (Asthma Control Questionnaire (ACQ)), asthma-related quality of life (Asthma-Related Quality of Life Questionnaire (AQLQ)), sino-nasal symptoms (Sino-Nasal Outcome Test (SNOT-20)), medication requirement, postbronchodilator (post-BD) forced expiratory volume in 1 s (FEV(1)), 6-min walking distance (6MWD), total immunoglobulin (Ig)E, blood eosinophils and exhaled nitric oxide fraction (F(eNO)) at admission and after 12 weeks. Sensitised and nonsensitised patients showed similar improvements in ACQ (-1.4 and -1.5, respectively; p = 0.79), AQLQ (1.6 and 1.5, respectively; p = 0.94), SNOT-20 (-0.7 and -0.5, respectively; p = 0.18), post-BD FEV(1) (6.1% and 5.8% pred, respectively; p = 0.87), 6MWD (+125 m and +147 m, respectively; p = 0.43) and oral steroids (40% versus 44%, respectively; p = 0.51). Sensitised patients showed a larger decrease in total IgE, blood eosinophils and F(eNO). High-altitude treatment improves clinical and functional parameters, and decreases oral corticosteroid requirement in patients with severe refractory asthma, irrespective of allergic sensitisation.