Clinical pharmacists play an important role in improving drug safety on hospital wards. However, little is known about the impact of pharmacy interns. The objective of our study was, therefore, to investigate the impact of hospital ward-based pharmacy interns on drug safety. This study was conducted as part of the project "P-STAT 2: Pharmacy interns on the ward" on 14 surgical wards in seven hospitals in Germany and a total of 27 pharmacy interns participated. All patients admitted to the participating wards from 1st June 2008 until 31st October 2008 and from 1st December 2008 till 30th April 2009 were included. The pharmacy interns were involved in medication reconciliation, and identifying, resolving, and preventing drug-related problems (DRPs) using the classification system APS-Doc. A total of 6,551 patients were included. Patients received on average (+/- SD) 4.4 +/- 3.9 drugs. The pharmacy interns detected a total of 4,085 DRPs and on average 0.6 +/- 1.2 DRPs per patient. Most frequently detected DRPs were potential drug-drug interactions (n = 591, 14%), missing drug strength, when different strengths were available (n = 373, 9%), and incomplete medication record (n = 296, 7%). The pharmacy interns conducted an intervention for 98% (n = 4,011) of all DRPs. According to their documentation, 74% of the DRPs (n = 3,038) were solved. Drugs which were most often related with DRPs were simvastatin, diclofenac, and ibuprofen. This is the very first study exploring the potential impact of pharmacy interns on drug safety on surgical wards in Europe. Pharmacy interns can play an important role to improve drug safety on hospital wards.