Medication errors occur very frequently. The limited knowledge of contributing factors and risks prevents the development and testing of successful preventive strategies. Objective: To investigate the differences between the ordered and dispensed drugs, and to identify the risks during medication. Methods: Prospective direct observation at two inpatient hospital wards. Results: The number of observed doses was 775 and the number of ordered doses was 806. It was found that from the total opportunities of 803 errors 114 errors occurred in dispensed drugs corresponding to an error rate of 14.1%. Among the different types of errors, the most important errors were: dispensing inappropriate doses (25.4%), unauthorized tablet halving or crushing (24.6%), omission errors (16.4%) and dispensing an active ingredient different from the ordered (14.2%). 87% of drug dispensing errors were considered as errors with minor consequences, while 13% of errors were potentially serious. Conclusions: Direct observation of the drug dispensing procedure appears to be an appropriate method to observe errors in medication of hospital wards. The results of the study and the identified risks are worth to be reconsidered and prevention measures should be applied to everyday health care practice to improve patient safety. Orv. Hetil., 2011, 152, 1391–1398.