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Asthma is a heterogeneous disease with high prevalence and a significant effect on quality of life. Severe asthma is notoriously hard to define, even more so for research. In this issue of the Journal, Mincheva et al (p 2256) propose a novel definition of asthma severity based on multiple signs, including daytime and nighttime symptoms, lung function, high degree of medication, and exacerbations. This algorithm was applied to a large-scale epidemiologic study, the West Sweden Asthma Study, and the following was concluded: Asthma severity phenotypes are exceptionally diverse and require individualized approaches to each asthmatic patient. Asthma severity is present in 13% to 36% of all asthmatic patients, depending on definition. Several factors are associated with asthma severity, most prominently smoking and obesity. In summary, every third asthmatic patient shows at least 1 sign of asthma severity, which is a clear indicator that there are still