Bronchiectasis is a common disease with important impacts on patient's quality of life and on healthcare systems in terms of healthcare costs, hospitalisations and mortality. After decades of being regarded as an orphan disease there are an increasing numbers of treatments available, or in late-stage clinical trials. Assessment of disease severity is fundamental to clinical management. To date, however, there is no agreed definition of what constitutes mild, moderate or severe bronchiectasis. These terms are often applied to radiological appearances, but while important, computed tomography findings are not sufficiently precise to capture the complex impact of the disease. Studies are beginning to define the risk factors for mortality, hospital admissions, exacerbations and impaired quality of life in bronchiectasis, allowing us to propose new definitions of what constitutes severe bronchiectasis. An improved understanding of severity and prognosis in this disease will aid clinical decision making and the application of new therapies.