QUESTION UNDER STUDY: Medication errors are a major concern for health care since they may cause or lead to inappropriate medication use or patient harm. However, little is known regarding the economic burden of unjustified medications. METHODS: Hospital discharge records of 577 patients were prospectively screened for the presence of unjustified medications. From this sample population, 318 (55%) were eligible and their data were used to assess the monthly costs of unjustified discharge medications, their relationship to the total and each individual's drug expenditure, and the relative cost weights of relevant unjustified drug classes. RESULTS: The results found that 619 out of 3691 prescriptions (16.8%) were unjustified. The mean (median; 95% CI) monthly costs of unjustified discharge medications were 32 euro (27 euro; 29 euro to 35 euro). The percentage of unnecessary treatments was inversely linked to the amount of total individual drug expenditure. For this collective, monthly extra costs due to unjustified medications were 18585 euro, and the relative cost weights of the relevant drug classes were 45.8% for gastrointestinal agents (33.8% for proton pump inhibitors), 17.7% for cardiovascular drugs, and 17.2% for psychiatric drugs. CONCLUSIONS: There is a considerable financial burden imposed by unjustified medications at hospital discharge. Discharge medications not motivated by appropriate diagnoses should be questioned. This study should be repeated in other institutions and in a larger population.