Rationale: Chronic Obstructive Pulmonary Disease (COPD) is increasingly recognized as a multi-component disease with systemic consequences and effects on quality of life. Single measures such as lung function provide a limited reflection of how the disease affects patients. Composite measures have the potential to account for many of the facets of COPD. Objective: To derive and validate a multi-component assessment tool of COPD severity which is applicable to all patients and healthcare settings. Methods/ Measurements: The index was derived using data from 375 COPD patients in primary care. Regression analysis led to a model explaining 48% of the variance in health status as measured by the Clinical COPD questionnaire with four components: dyspnea (D), airflow obstruction (O), smoking status (S) and exacerbation frequency (E). The DOSE index was validated in cross-sectional and longitudinal samples in different healthcare settings in Holland, Japan, and the United Kingdom. Main results: The DOSE index correlated with health status in all datasets. A high DOSE index score (> = 4) was associated with a greater risk of hospital admission (odds ratio 8.3 (4.1 - 17) or respiratory failure 7.8 (3.4 - 18.3). The index predicted exacerbations in the subsequent year (p 0.014). Conclusions: The DOSE index is a simple valid tool for assessing the severity of COPD. The index is related to a range of clinically important outcomes such as healthcare consumption and predicts future events.