When medicine different from the prescription was given to patients or medical staff, we analyzed the occurrence factors for the incident, took measures to prevent such errors, and evaluated the effectiveness in Kyushu University Hospital. There are many reports on the prevention of dispensing errors in various medical institutions. However, there has been no report analyzing the relationship between the classification of dispensing errors (wrong number, wrong preparation, wrong medicine) and the impact on patients.<br>In this study, we calculated the annual 'impact score' and 'risk score' based on the impact on patients and the classification of dispensing errors, respectively. Then, we analyzed the relationship between both scores using the correlation coefficient, and estimated the 'risk ratio' for the classification of dispensing errors. As a result, the risk ratio was estimated as 1:6-7:8, 1:6-8:9, and 1:7-9:10 for wrong number, preparation and medicine, respectively. This may be useful for pharmacists to raise awareness of serious incident prevention.