Adverse drug events (ADEs) are a considerable cause of morbidity and mortality in hospital practice. The precise frequency is unknown, but studies give an incidence number ranging from 2 until 52 ADEs per 100 patients. There are many different methods for definition, causality assessment, severity classification and detection which make it difficult to compare the different studies. A substantial part (in some studies up to 70%) of ADEs can be prevented and it is important to, besides their detection, focus on the prevention of these ADEs. In this literature review we give an overview of methods for preventing ADEs. There are many different tools with different impact on a particular part of the distribution system which has the potential to prevent ADEs. A multifaceted approach is needed. Two interesting strategies of prevention, pharmacist participation on ward rounds and computerised physician order entry with clinical decision support systems (CDSS), are highlighted. Moreover, two promising CDSS are discussed in more detail, namely computer-based monitoring systems and information systems which link laboratory and pharmacy data.