Adverse drug reactions constitute a major health concern for the individual patient and the community. However, most reports on adverse drug reactions in Europe depend heavily on extrapolations based on incidence estimates from US studies. In order to explore the epidemiology of adverse drug reactions in Switzerland, we set up a pharmacoepidemiologic database on medical inpatients at the University Hospital Zurich and the Kantonsspital St. Gallen and monitored so far over 10000 hospitalisations for drug utilisation and adverse drug events. 4.1% of all admissions were caused by adverse drug events. About 1/3 of them were caused by medication errors, whereas the remaining represented non-preventable adverse drug reactions. 7.5% of the patients experienced an incident adverse drug event during hospitalisation and 1 among 20 of these were caused by medication errors. So far, we also have explored the epidemiology and characteristics of selected adverse drug reactions, such as for example drug-induced liver injury, NSAID-associated gastrointestinal bleeding and a potential drug interaction between paracetamol and phenprocoumon. These findings and the strength and limitations of such databases will be discussed.