Even in industrialized countries, health care is not as safe as it should be. The term "patient safety" denotes the non-occurrence of adverse events and the presence of measures to prevent them. The literature was selectively reviewed to obtain information on the epidemiology and causes of preventable adverse events (PAE), as well as on measures that can increase patient safety. Preventable adverse events occur in Germany both in the hospital and in outpatient settings, although their precise frequency is currently a disputed matter. PAE should be analyzed systematically. They are caused both by active errors and by latent failures that are inherent in components of the health care system. Three main strategies should be pursued to improve patient safety. A safety management system involving error reporting, learning from errors, and the fair exchange of information should be established in hospitals and in doctors' outpatient practices. An error management system should be implemented in which critical incidents are identified, reported, and analyzed so that similar events can be prevented, and measures for the prevention of critical incidents and errors should also be implemented and evaluated. Finally, whenever preventable adverse events do occur, the persons involved should take action to prevent further harm to the patient and other involved individuals.