The electronic medical record is gradually penetrating the world-wide healthcare environment, including Korea. Users of electronic medical record want to get full advantages of it, but benefits would not be realized by simple implementation. Wellorganized architecture and controlled medical vocabulary are needed for achieving effective electronic medical record system. Many terminologies are introduced in healthcare system but single noble terminology to cope with users' need is not present. To extract clinically useful and standardized set of chief complaints for electronic medical record in our institutional environment, we analyzed chief complaints in 235,426 discharge summaries in Seoul National University Hospital. We normalized the chief complaint by 27 medical experts. First of all, researchers parsed chief complaints as main concept, qualifier, and modifier. We normalized main concepts, keeping applicability and usability of extracted set to electronic medical record in mind. And then, mapping set of chief complaint to SNOMED CT was done by 4 physicians. Among 94,913 unique strings, we selected 6,317 terms as standard set of chief complaint. The potential users of electronic medical record were asked to evaluate usability of the set and accepted it as representative of chief complaint. The majority of terms in set were completely mapped to SNOMED CT. We discussed several principles in normalizing chief complaints. We also pointed pros and cons of SNOMED CT as reference terminology to chief complaint domain. Through this study, we developed conceptually standardized chief complaint domain with user-friendly terms in Seoul National University Hospital Environment. Furthermore, this result would be the starting point to evolve medical terms in Korea into ontology based terminology system.