In the UK, medication errors are a growing problem. Dobrzanski et al (2002) estimated that in one trust the incidence of medication error ranged between 35 to 70 per cent. Such high estimations are a cause for concern, particularly when the administration and supply of medicines, which directly involves nurses, can contribute to the cause of medication error. Part of the National Patient Safety Agency’s (NPSA) role is monitoring medication errors in hospitals. Although the NPSA can provide information on drug alerts that target primary care organisations, obtaining accurate figures for medication errors is more difficult. Medication errors can be extremely harmful for older people, therefore nurses who prescribe or administer medicines should be assessed for mathematical competence, but also be aware of the potential problems that can arise from medication errors (Banning 2005).