Purpose: Clinical performance examination (CPX) using standardized patients (SPs) is an acceptable method of testing medical professionals, but there has been some concerns about security. The objective of this work is to examine whether the day of the examination influences the scores of examinees of different medical schools at different times throughout the examination period. Methods: Six medical schools, which had participated in the Seoul-Gyeonggi CPX Consortium 2005, were enrolled. Each station, controlled by the same regulations, included 12 minutes of SP encounter and 5 minutes of writing a short essay. We compared the mean scores using ANOVA and linear trends with multiple regression analyses and SPSS version 11.0. Results: The mean score of examinees from all 6 medical schools was 63.2±6.9. There was no difference in total mean scores among the medical schools according to the period when CPX was conducted. Classified by their examination day, there was no difference among the mean scores of the 1st, 2nd, and 3rd day, but in one school where the examination was performed for 5 days, the mean scores of the 4th day was higher than the others (p<0.05). There were trends of linear increases over the five days for the ‘physical examination’question, but not for ‘physician-patient interaction’and ‘patient education’. Conclusion: The changes in scores according to the examination day in this study did not show consistent results. However, the variable results seen according to school, test question, and examination day need further analysis for test security issues.