In October 2003, the Department of Pharmacy in Kyushu University Hospital obtained ISO9001 certification for the quality management system of the pharmacy practice in order to promote effective and safe pharmacotherapy for patients. We introduced this system in April 2005 to prevent dispensing errors for narcotic drugs. When the wrong medicines were given to patients, we analyzed the factors for the dispensing errors, took corrective and preventive actions to prevent such errors, and evaluated their effectiveness later.<br>In this study, we analyzed the number, classification and environmental factors for the dispensing errors for narcotic drugs, and evaluated the usefulness of measures for preventing the errors based on the ISO9001 quality management system. As a result, since the introduction of the management system, the dispensing errors and incidents have remained below 0.1% and 0.025%, respectively, although the number of adopted narcotic drugs has been increased. These results suggest that the ISO9001 quality management system is useful for the prevention of dispensing errors for narcotic drugs.