1. Errors will always occur in any system, but it is essential to identify causes and attempt to minimize risks. 2. Although it is difficult to quantify precisely the extent of medication errors, they are clearly frequent and often avoidable, representing a major threat to patient safety. 3. Many of the consequences of these errors can be prevented by the intervention of pharmacists. 4. Some errors are due to the conditions under which prescribers work; where possible these should be improved (for example, low staffing levels). 5. Computerized prescribing can help but can also generate its own inherent errors. 6. Improved training of prescribers at the undergraduate and postgraduate levels is vital, a fact that is now being belatedly recognized.