Purpose: The purpose of this study is to analyse the gap between what medical students learn in theory and their clinical performance in reality. The hypothesis is that students with high written examination scores will also perform better in the Clinical Performance Examination(CPX). Methods: 128 Catholic University medical students in year four took the CPX on 24th, September 2005. 40 standardized patients (SPs) were involved as assessors. Each student performed five CPX cases. The students written examination scores of year three, SPs assessment scores were used as instruments. Students were divided into two groups (A and B) and each group consisted of 64 students. Correlation between the written examination scores and the CPX scores, CPX case scores and related written examination scores were analysed. Results: Overall, there was no significant correlation between the CPX score and the written examination scores in total, but significant correlations were shown in family medicine CPX scores of both groups A and B (pearson=.308, p=.199; pearson=.258, p=.051). From the analysis of the CPX cases and related written examination scores, group A showed significant correlation in three out of the five cases. No significant correlation seen in group B. Conclusion: It can be concluded that large gaps still exist between theory and practice. Some suggestions are given to minimize these gap.