A medical expert system for the diagnosis of abnormal vaginal bleeding named as ABVAB had been reported. This paper will describe the recent development of ABVAB and its clinical evaluation. The overall testing results are quite satisfactory in spite of the limitations of time and small domain. This expert system, by using the fuzzy and certainty factor concepts, is able to handle imprecise and incomplete medical knowledge which has become informative. The paper also analyses the relative degrees of importance of the history and physical examination data in making a medical diagnosis.