In 1994, Ajou University Medical Center implemented a hospital information system with a relational database management system(Ingres) and underwent migration using newly improved M technology in 1996. In this paper, a comparison study of database performance between M and RDBMS is presented. Three different types of comparative studies were carried out on the performances of Ingres, Oracle 7.1 (Oracle) and M-Technology(Mumps). Two types of M are adopted to compare with Ingres: Standard M and Open M. The open M was used for DBMS and Standard M was used for writing applications. The system response time was compared by a simple bulk test in a simulated HIS environment. It was found that the performance of Open M was about 100 times faster than that of Ingres. In the live HIS environment, the performance of Open M was found to be 2-8 times faster than Ingres depending on the number of globals involved in the processing of transactions. The performance of Standard M and MSM-SQL was compared with that of Oracle by a simple bulk test in a simulated HIS environment and found that Standard M was more than 100 times faster than Oracle and MSM-SQL was on an average. 1.7 times faster than Oracle. The M was faster than Ingres and Oracle. Despite the cons of RDBMS already discussed, we have found very few pros of RDBMS if M is applied. We have found that conventional RDBMS requires redundant hardware resources which result in slow processing time which HIS manifests in a serious bottleneck during the course of our development and implementation. The performance of M strongly implies that M is most appropriate DB in a HIS environment.