Objectives To determine the frequency and nature of erroneous transfer of medication information (medication errors) upon admission to hospital and to study the effect of medication reconciliation.

Methods Included patients were 65 years of age or older, were living in nursing homes or in their own home with care provided by the community nursing system and had been admitted to hospital. The patients’ medication lists from the community were compared with the hospital medication lists upon admission in order to study the discrepancies between the lists. The proportion of errors that were corrected by day 4 of hospitalisation was also studied as a measure of the effect of medication reconciliation conducted by clinical pharmacists who aimed to identify the patients’ accurate and complete medication history.

Results A total of 149 patients were included over a 10-month period. In 68 (46%) patients, there occurred at least one medication error, with an average of 0.95 errors per patient. Overall, 8.0% of all drug transfers were found to be incorrect. The clinical pharmacists detected all medication errors upon admission and 43% of them were corrected before day 4 of hospitalisation.

Conclusions Medication errors upon admission to hospital are common; use of clinical pharmacists in the admission medication reconciliation process appears to be a useful method to reduce medication errors, but since our study lacked a control group further studies are needed to show the actual impact of pharmacist-led medication reconciliation upon admission to hospital. Furthermore, more actions are needed to enhance the safety and quality of medication information transfers.