BACKGROUND: Redispensing unused medications that have been returned to outpatient pharmacies by patients may reduce waste and healthcare costs. However, little is known regarding the extra costs associated with this process, nor the price level of medications for which this is economically beneficial. The objective of this study was to assess costs associated with redispensing unused medications in the pharmacy and the price level at which redispensing becomes cost-beneficial. METHODS: A micro-costing study was conducted in four Dutch outpatient pharmacies for medications requiring room-temperature storage and requiring refrigeration. First, the pharmacy's necessary additional process steps and resources for redispensing were identified. Second, time required for each process step was simulated. Third, required resources were quantified by calculating labour, purchasing and overhead costs. Lastly, a model with different scenarios was constructed to calculate the price of a medication package at which redispensing becomes cost-beneficial. RESULTS: Three main additional process steps for redispensing were identified: (1) pack medications with product quality indicators before dispensing, (2) assess quality of medications returned to the pharmacy (temperature storage, package integrity, expiry date) and (3a) restock medications fulfilling quality criteria or (3b) dispose of medications not fulfilling criteria. Total time required for all steps up to restock one medication package was on average 5.3 (SD ±0.3) and 6.8 (SD ±0.3) minutes for medications stored at room-temperature and under refrigeration, respectively, and associated costs were €5.54 and €7.61. Similar outcomes were found if a medication package would ultimately be disposed of. The price level primarily depended upon the proportion of dispensed packages returned unused to the pharmacy and fulfilling the quality criteria: if 5% is returned, of which 60% fulfils quality criteria, the price level was €101 per package for medications requiring room-temperature storage and €215 per package for those requiring refrigeration. However, if 10% is returned, of which 60% fulfils the quality criteria, the price level decreases to €53 and €109, respectively (arbitrary proportions). CONCLUSIONS: Redispensing unused medications in the pharmacy is at least cost-beneficial if applied to expensive medications.