Trauma patients, who often suffer severe, multiple injuries and undergo multiple handoffs during long hospital stays, are particularly vulnerable to medication errors. This observational, descriptive, prospective study comprises an analysis of the medication errors that occurred during care transitions for all patients admitted to the trauma service unit of a hospital in Madrid, Spain over a four-month period. Results indicate that most medication errors occurred in the trauma unit and 64.2% of these types of errors were detected during the medication reconciliation process.