Primum non nocere (first, do not harm) remains a basic tenet of medical practice. Unfortunately, the complexities of modern medicine, the large pool of available medications as well as the multiplication of technical procedures combined with the frequent difficulty of reaching definite diagnoses and the high number of medical professionals taking care of a single patient have resulted in a growing number of medical errors, a significant part of which prove fatal for the patient. Data on the number of deaths caused by medical errors are not readily obtainable, nevertheless a number of recent studies in the US have reported figures greater than 200,000 deaths per year. For example, a patient safety expert team from John Hopkins University has calculated that over 250,000 deaths are caused by medical error in the US, based on an analysis of medical death rate data over an eight-year period. This figure was published last May in the BMJ and places medical error as the third highest cause of death, accounting for 10% of all US deaths. For the healthcare industry, this translates into about six potentially preventable deaths per year per US hospital, definitely not good statistics. The situation is somewhat similar in Europe, even if there aren’t any official figures at the EU level as Eurostat doesn’t list medical error as a possible cause of death since its statistics – like those of the US CDC – rely on the medical information contained on death certificates and on the coding of causes of death according to the WHO International Classification of Diseases (ICD) codes. Results from German studies on patient safety show that close to 20,000 deaths are caused by preventable adverse events in the country’s hospitals. These deaths cover a wide range of preventable causes, including hospital-acquired infections, embolisms, surgical errors, delay in diagnosis (especially for pediatric patients) and misdiagnosis – the latter probably ranking quite high even if very difficult to detect in research. Apart from deaths, there is a much bigger number of cases, up to 20-fold higher, where people suffer from serious adverse effects, sometimes for the rest of their lives. In addition to the individual harm incurred, there is also a high cost for society that includes additional healthcare expenditure, social costs and loss of economic capacity. Evidence shows that up to 70% of the harm caused by medical errors can be prevented through comprehensive systematic approaches to patient safety. At the hospital level, there is an urgent need for action, not least by physicians – they should be the first to recognize that every single death caused by a preventable adverse effect is one too many.