Since synonyms are provided for the articles in addition to descriptors in the Igaku Chuo Zasshi CD-ROM edition of the Iaku Yogo Thesaurus, searchers can use not only descriptors but synonyms in thesaurus searching. In the descriptions in the Igaku Yogo Thesaurus, however users must search by descriptors not by synonyms. This is inconsistent. In this paper, we assessed the validity and the inconsistencies of the Igaku Yogo Thesaurus, Ultimately, the validity of Igaku Yogo Thesaurus was recognized, but a clear distinction between descriptors and synonyms may be necessary.