Since the publication of the report ‘To err is human’ by the Institute of Medicine (IOM) in 1999, public attention was drawn to the importance and magnitude of the issue of patient harm from medical errors. Patient safety is defined by the IOM as a subset of quality of care and focuses on the way in which risks on unintentional and evitable harm to the patient are handled in the organization of care. Patient safety should be the top priority in every healthcare organization. Still often, it is not enough in the attention of healthcare professionals and organizations. Lack of awareness of the severity of the problem, the complexity of healthcare organizations and the lack of data as a result of the paucity of measures are important barriers for improving safe care. Improving patient safety in healthcare organizations needs a system approach integrating different methods, such as the assessment and improvement of the safety culture, adverse events detection, analysis of the root causes and contributory factors of adverse events, prospective risk assessment, the implementation of improvement strategies and the education and training of healthcare staff. Although, patient safety is receiving growing attention, there is scarce evidence on estimations of adverse events in Belgian hospitals. In addition, safety culture has not been measured on a broad scale in order to provide a basis for improving patient safety systematically in Belgian hospitals. Therefore, the primary objective of this dissertation was to fill an important gap in the current research on patient safety and safety culture in the Belgian hospitals. A secondary objective was to help hospitals to understand the nature of the safety culture within their organizations in order to implement strategies for improving patient safety. First, a systematic review was conducted to estimate the incidence and preventability of adverse events that have a high impact for the patient, the hospital and society. The next phase built further on the available evidence and ...