Gachon Medical School used an oral examination in the pathology course taught during the 2nd semester of the 2000 school year as a performance assessment of students abilities in three areas: comprehension, logic and problem solving. The evaluation instrument was designed in four stages: assessment objectives were determined, abilities to be measured were selected, the assessment instrument was designed, and the examiners checklist was drafted. The assessment instrument included two gross and two microscopic cases and the checklist was developed using 5 Likert type scales. The students were divided into three groups of 12 to 13 students and two examiners were allocated to each group. The mean score on the oral examination was 3.56 (the highest possible score is 5.00). The correlation between examiners was 0.952 while the correlation of gross and microscopic cases was 0.979. Obviously, these data are statistically significant. The correlation between the written examination pathologic-laboratory examination was the highest, that between the oral examination and pathologic-laboratory examination was in the middle, and that between the oral examination and the written examination was the lowest. Students expressed doubts about the objectivity of individual examiners. The high correlation between the examiners scores and how students scored on other tasks shows that students fears can be assuaged. It is concluded that the oral examination is a powerful tool in measuring students ability, and can be used in a basic medical science course. As an assessment instrument, it is both valid and reliable.