Differences in hospital staffing may influence outcomes for patients with acute conditions, including acute exacerbations of chronic obstructive pulmonary disease (COPD), depending on which day of the week the patients are admitted. This study was conducted to determine whether weekend admission increases the risk of dying in hospital.We analysed the clinical data of 289,077 adults with acute exacerbations of COPD admitted to the hospital at any public centre in Spain, during 2006 and 2007. We analysed the following factors for their association with death rate: day of admission, demographics, medical history and comorbidity.During the study period, there were 35,544 (12.4%) deaths during admission in COPD patients. Weekend admissions were associated with a significantly higher in-hospital mortality (12.9%) than weekday admissions (12.1%) among COPD patients (OR 1.07 (95% CI 1.04-1.10)). The differences in mortality persisted after adjustment for age, sex and coexisting disorders (OR 1.05 (95% CI 1.02-1.08)). Analyses of deaths within 2 days after admission showed larger relative differences in mortality between the weekend and weekday admissions (OR 1.17 (95% CI 1.11-1.23)).We conclude that patients with acute exacerbations of COPD are more likely to die in the hospital if they are admitted on a weekend compared with a weekday.KEYWORDS: Chronic obstructive pulmonary disease, mortality, weekend effect A cute exacerbations of chronic obstructive pulmonary disease (COPD) are among the leading causes of morbidity and mortality in industrialised countries [1,2]. ,10% of all hospitalisations are either directly or indirectly attributable to COPD [3], and internal medicine [4] and respiratory wards care for many patients with this disease. Acute exacerbations of COPD requiring hospital treatment are a severe strain on health services and are responsible for at least two-thirds of the total cost of treating respiratory diseases in both Europe and the USA [5]. The acute exacerbation phase entails a substantial rate of hospital mortality [6]. The recognition of risk factors for mortality among patients hospitalised for COPD can be of crucial importance for curtailing cost and reducing mortality.Several studies [7][8][9][10][11][12] concluded that weekend hospitalisation is associated with worse health outcomes. These studies are supported by the work of others [13,14], which find a positive correlation across hospitals between annual average staff-to-patients ratios and quality of care. While the burden of disease and demand on health services is similar from one day to the next, at the weekend, there are staff shortages and reduced availability of services. Unfortunately, this might not be compensated for by increased care on subsequent days.The weekend effect on COPD has been specifically studied in a recent Australian study [15] by a retrospective analysis of administrative data from public hospitals, analysing the 30-day inhospital mortality in 30,000 patients; no significant weekend effect was detected. Ho...