Fibro-osseous lesion(FOL) has been known a lesion that normal bone is replaced by cellular fibrous connective ti ssue and nonfunctional bone, FOL has been classified and revised by several investigators and World Health Organization(WHO) , For correct diagnosis and treatment, it is necessary to classify FOL precisely, Compared to the class ificat ion by WHO in 1992‘ the new version of 2005 makes it simpler to classify , Therefore, the aim of this study is classifying FOL by the WHO classification in 1992 and compare it with the new ve1'sion in 2005 The material was 1'e tl‘ ieved f l'om the cases which were diagnosed as FOL from 1992 to 2005 in the Department of Oral Pathology, Yonsei University College of Dentistl'Y, Clinical, rad iological and pathological observations were conducted for this study Comparing WHO classifi cation in 1992 with the one in 2005, there were no differences regarding clini cal, radiological a nd hi s tological f indings in each classified disease entity of both osteogenic neoplasm and non neoplastic bone lesion , Hence, the new classification by WHO in 2005 would be a useful yardstick for correct diagnosis and treatment , For the differential diagnos is between osteogenic neoplasm and non neoplastic bone lesion, it is important to observe the degree of cell ularity microscopi cally and definiteness of the border radiographically,