Paget's disease of bone (osteitis deformans), a chronic osseous disease of unknown etiology, is extremely rarein Asia although well known in western countries. This disease is characterized by the simultaneous absorption ofbone and the new bone formation of abnormal character affecting middle and later age groups. The authorsexperienced a case of monostotic Paget's disease involving left pelvic bone in 56-years old female. To ourknowledge, this is the first cas report of monostotic Paget's in Korea.