OBJECTIVES: One of the main policy targets in many European health care systems is to provide constant quality of health care across time and space without discrimination of patients. Many studies show that the risk of mortality after admission to a hospital following acute diseases such as stroke is significantly higher on weekends than on weekdays. However, from a medical point of view the burden of disease should be consistent throughout the week. Literature calls this phenomenon weekend effect, which has caused great attention by experts and the public since the 1970s. The independent effect has been found in all inpatient settings of care irrespective of elective or emergency care. The weekend effect is well documented, however the reasons are still discussed controversially. Evidence for variation of health outcomes overnight, at holidays or at the weekend is still scarce and in many cases speculative. This study aims to analyse whether there is constant service quality measured by health outcomes in inpatient care across weekdays when controlling for patient and hospital characteristics in Austrian acute care hospitals. *** METHODS: The study analyses secondary datasets from all public acute care hospitals in Austria from 2010 to 2014 (Austrian DRG Data). The study cohort includes all patient episodes suffering from acute ischaemic stroke admitted to public Austrian acute care hospitals (approx. 88,500 episodes in 130 hospitals). The data sources contain patient characteristics and aspects of quality of care allowing a retrospective study by performing multivariate regression analysis controlling for important patient-level as well as hospital characteristics. The primary outcome variable is case fatality rate within 30 days after admission to an acute care hospital and the primary independent variable is admission on weekends (Saturday, Sunday, and holidays) versus weekdays. *** RESULTS: Admissions following stroke on weekends are significantly lower than on weekdays. At the same time, the risk to die after an admission at a weekend is significantly higher. The results show a significant weekend effect on stroke mortality. Hospital as well as patient characteristics on weekends differ significantly with regard to treatment, patient demographics, infrastructure and staffing. The weekend effect might be attributed to higher stroke severity in weekend patients (case mix on weekends) but further analysis and rigorous risk adjustment is needed to show clearer evidence. *** DISCUSSION: Patients admitted to Austrian acute care hospitals following stroke show a higher mortality than patients admitted on weekdays. Disparities in quality and patient characteristics may explain the observed differences in weekend mortality. The dataset allows only the calculation of covariates that mix quality and severity proxies which makes a clear attribution challenging. The findings should initiate further research and critical evaluation whether resources, expertise and staff should be provided for critical care in the same quantity and quality throughout the week.